A .770 pct would give them 118.5 wins in a 154 game season.
One reason that they did not win more is that they may have scored fewer runs than expected based on their OBP and SLG. Here is the regression generated equation for runs per game during the 1920s for all teams:
R/G = 11.29*SLG + 18.04*OBP - 5.92
The Yanks had a .489 SLG and a .384 OBP. That predicts 6.53 runs per game while they actually had 6.29. Over the whole season, that is about 37 runs fewer than expected. Out of the 160 teams in the decade, the 27 Yanks were 10th in underscoring.
So maybe that accounts for about 3.7 wins. That still leaves about 4.8 wins.
But why did they not score more runs? They stole 90 bases, just a bit below the league average of 99. Their success rate was 58.4%, just a bit below the league average of 60.7%. This probably does not matter much.
Maybe they had too many sacrifice bunts. They had 107 according to Retrosheet. But the other 7 teams averaged 148. So I doubt they lost alot of big innings bunting too much.
Their pitchers allowed an SLG of .356 and an OBP of .320. The regression equation for runs allowed was:
R/G = 11.25*SLG + 18.68*OBP - 6.12
That predicts they would allow about 3.86 runs per game, their actual total. So they did not win fewer games than expected due to the pitchers giving up more runs than expected.
Here are the splits for the Yankee hitters and pitchers followed by the league splits. Nothing jumps out as to why they won fewer games than expected. Maybe that they did not hit better with runners or on with RISP like the league generally did. That might account for them not scoring as many runs as expected.
I don't see anything in their close and late performance that explains anything. It even looks like their pitchers did a very good job then compared to what the league did.
They were also 24-19 in 1-run games for a .558 pct. That means they were .775 in all other games. (if they had done as well in 1-run games as they did at other times it would mean 9 more wins)
|Close & Late||0.287||0.370||0.460|
|Close & Late||0.224||0.275||0.288|
|Close & Late||0.266||0.332||0.365|
The Yankee pitchers had an AVG allowed when it was close and late 41 points below their total AVG allowed. The league as a whole had 20 points. It seems like they would have done well in 1-run games because of that. Their hitters did about what you would expect in close and late situations when you look at the league stats.
So the fewer runs scored explains a good chunk of the missing wins, but it is not clear what explains the rest.