So when and how did losing 20 become such an embarrassment?
There were a number of factors that helped do away with the high-loss pitcher. First, the most immediate was the 1981 strike the year after Kingman lost 20. That year there were a number of pitchers who were on a pace to lose 20 but did not come close due to the strike that wiped out one-third of the season.
Here are the major-league leaders in losses in 1981 with the number of games their teams played and their losses projected over a 162-game schedule. (Note that pitchers on multiple teams had their teams' number of games averaged: Koosman, Minnesota (110) and ChiSox (106) and Berenguer, KC(103) and Toronto (106).)
So we'll never know if all or any of the possible six pitchers projected to reach 20 losses would have done so if the season had not been interrupted. However, it is a good indication that Kingman's 1980 season in itself did not mark a drastic change in the use of pitchers.
There were also some pitching trends that came to a head coincidentally soon after Kingman's 20-loss season. In the early Seventies, teams started switching to 5-man rotations. While this may seem to limit the number of starts for pitchers and therefore the number of potential losses, what it really did, at least initially, was given the top starters more starts (sometimes in the 40s, like we saw with Niekro) and set expectations for more innings out of individual pitchers. Both of those things helped retard the seemingly natural progression in baseball to greater specialization on pitching staffs and therefore fewer complete games and more sharing of innings, wins, and losses. This helped keep the number of twenty-game losers artificially high into the seventies.
In 1979, Bruce Sutter put on the finishes touches on the definition of a modern reliever. I believe that the closer helped ensure that starting pitchers won a greater number of games or at least decreased the number of blown leads by starters who were tiring. Therefore, it got more difficult to snatch defeat from the jaws of victory.
Lastly, the expansion of the Sixties and Seventies helped keep the number of 20-game losers high as extremely poor clubs and extremely poor pitchers were admitted into the majors. This began to be mitigated in the early Eighties.
So it seems that there were a number of trends that converged on the Eighties and have made it more difficult to lose 20 ever since. But could it have suppressed their number to such a degree that there have not been any 20-loss men in over twenty years?
I think that a stigma got associated with losing 20 in the mid-Eighties that had not existed before. I believe that managers proceeded to remove potential 20-game losers from the rotation to spare the players the embarrassment of such a dubious distinction. This lasted, I believe, until Omar Daal came within one loss of 20 in 2000 with the D'Backs and Phils. Let's check if this is true with some pitchers who came close to losing 20 (By the way, the research for this was conducted with data from the incomparable Retrosheet site):
In 1982, Bruce Berenyi went 9-18 for the Reds with a 3.36 ERA. He stayed in the rotation the entire year and even though he already had 18 losses he made his last two scheduled starts (winning a complete game 2-0 shutout and getting a no-decision in the second, a 3-2 loss).
Frank Tanana went 7-18 in 1982. He lost 5 straight decisions between August 29 and September 15. He won his last game September 20. He didn't pitch in the last twelve games the Rangers played but it appears that they gave his turn to youngster John Butcher to see what he could do. Possibly removed to avoid 20 losses.
Matt Keough was 11-18 in 1982 and he made all his starts even though he was at 18 losses with two starts to go.
In 1983, Larry Gura finished at 11-18. He was removed from the rotation after an outing that lasted 3.2 innings in which he gave up 8 hits, 6 runs, and 5 earned runs (his ERA stood at 5.08). His record was 10-17, but it appears that he was switched to the bullpen to work out exorcise his pitching demons (he had a 6.04 ERA in his last ten starts). He was switched back to the rotation after pitching 7.2 scoreless innings in three appearances (and winning one game), He lost his last game September 27.
In 1984, Jeff Russell, later a closer, was 6-18 but did so by losing six of the last eight games he started (plus a win and a no-decision) and he pitched until the end of September.
Also in 1984, "Headly" LaMarr Hoyt went 13-18, after winning 24 ballgames the previous year. He pitched the entire year in the rotation.
In 1985, Danny Darwin stood at 7-16 with a 3.58 ERA on September 3 with more than a month of ball remaining. He was pulled from the rotation after one more no-decision and pitched in the bullpen for the rest of the year, even though he has 11 complete games in 29 starts. He finishes eight of the ten games that he appears in as a reliever and save two. He finishes at 8-18 with a 3.80 ERA.
Also in 1985, Jose DeLeon was 2-18 on September 16 for the Pirates. He was then removed from the rotation and finished at 2-19. He is converted to the team's closer and finishes the game in each relief appearance he makes (5), along the way saving three.
Finally, Matt Young finishes at 12-19 in 1985 and stays in the rotation all year, but omly reaches 19 by losing the last four games that he pitches.
In 1986 Rick Mahler starts 39 ballgames and finishes 14-18
In 1987 Danny Jackson was 8-18 with two starts left. He made both starts and won one and got a no-decision in the other. Mark Gubicza finished 13-18 but started the entire year and was never in any danger if losing 20. On September 20, Mike Moore stood at 7-19 with two starts to go. He made each start and won both games. Tom Candiotti went 7-18 but made all of his starts
In 1989 Doyle Alexander went 6-18 in his final year, made all his starts, and was never in danger of losing 20. Walt Terrell went 11-18 with two clubs but made all his starts and won his last two games.
In 1990 Allan Anderson went 7-18. On September 7, he shut out the Indians to run his record to 7-17. He then did not pitch for two weeks. He pitched two more ballgames and was 0-1. Anderson may have been hurt (there's no DL in September) but there is a good chance he was held out to miss losing 20. He had been their staff ace in 1989, and for him to lose 20 may have been an embarrassment.
Jack Morris stood at 11-18 on September 12, 1990, but pitched and won his last four starts of the season to finish 15-18. Also in 1990, Jose DeLeon lost 19 games again but had to loss his last 7 starts to do so. Matt Young finishes 8-18 but has to lose his last 4 starts to do so.
On September 19, 1990, Tim Leary falls to 9-19 with a 4.11 ERA and does not pitch the rest of the year.
On September 4, 1991, Kirk McCaskill falls to 10-18 with a 4.19 ERA. He does not pitch for over three weeks and then loses his last start to record 19 losses.
By the 1993 All-Star break, the Mets' Anthony Young has fallen to 0-12. He then is used as a reliever. He finally wins a game to go to 1-13 and finishes the year as a reliever with a 1-16 record.
Also in '93, Doug Drabek logs a 9-18 record, but has to lose his last two decisions to do it. Scotty Erickson falls to 8-19 on September 18, but makes his last two starts and gets no more decisions for the year.
In 1996, Jim Abbott was 2-18 but never came close to losing 20. He did lose two games in Vancouver when he was sent down for a short time.
In 1999, Steve Traschel fell to 8-18 on the last day of the season.
In 2000, Omar Daal went 4-19 for Arizona and Philadelphia. On September 16 he was 3-19. Daal made two more starts and did not record a loss (the last game of the season was technically his turn and he did not pitch).
In 2001 Albie Lopez finished 9-19 with Tampa Bay and Arizona. He did not miss a turn in the rotation. Bobby J. Jones finished 8-19 without missing a turn as well.
In 2002, Tanyon Sturtze finished 4-18 for the D-Rays but stayed in the rotation all year.
So what does this all tell us? Well, that it is very hard to verify that anyone has been kept out of games to avoid losing 20 games. Perhaps a couple of players were at the start of the Nineties. But the Phils acted as if keeping Daal in the rotation was breaking new ground.
A pitcher who can lose 20 games is usually pretty good and can therefore turn around his season. There have probably been many other pitchers than the ones I listed above who were on track to lose 20 at some point into the season, but they were quickly replaced in the rotation, not because they would lose 20 games but because they were not pitching well and the team found someone they though could do better.
I think Maroth is good enough and the Tigers are bad enough to allow him to lose 20. However, a man with a 1.13 WHIP should be able to win some games along the way. I think Maroth comes close but no cigar. Better luck next year.