[babypuncher]

I don't think that is a good metric. There are far more single player games available on Steam than multiplayer.

A multiplayer lives and dies by its community, so it makes sense that multiplayer gamers would coalesce around a relatively smaller number of games.

Multiplayer games are also designed far more around player retention. The unpredictability of human opponents, combined with various design decisions meant to keep players engaged, means that a multiplayer gamer may primarily play the same game for years. A solo player reaches the end of their game, maybe they even exhaust all the side content and achievements, but then they move on to the next single player game.