The charts below are histograms that show the number of players divided up according to their quitting patterns. Players who rarely quit - between 0 and 10% of their games - are "bucketed" in the first column. Players who quit a lot - 90%-100% of their games - are bucketed in the last column. The rest are divided into buckets between those percentiles.
Private tables are ignored in these statistics, as are tables with only a single human player. Quitting from such tables is not a major problem. On the other hand, if you enter a game and then quickly leave, you are getting counted as a quitter for the purpose of these statistics. So the charts may make things look a little (or a lot?) worse than they are.
Hearts is badly hit by quitters. Hearts games are not usually very lengthy, and I suspect this game is one where people quit because they want to avoid a loss.
Spades is also pretty badly affected by quitters. I've noticed that people will sometimes quit when their bid is set (especially if it's a nil bid), or when they get set because they couldn't cover their partner's nil bid. Maybe they fear their partner's ire? I've also noticed people quitting when they are close to losing, here.
Euchre is a fairly quick game - you are usually done in 10 minutes. Quitters are not as big a problem, here.
Twenty-Nine has a huge problem with quitting. However, it's perfectly understandable - it's a game that can take several hours, as the scores of each team ebb and flow. This is just the nature of the game. So far as I can tell, many people enjoy this game, despite the fact that you often just have to quit to get on with your life. It's interesting.
Gin Rummy has statistics that are similar to Euchre. I'm not sure why. It's a 2-player game so it does tend to take less time.