Not him, but IIRC back when Steam Spy was a thing it discovered that most accounts on Steam only have one game on it. Usually Dota 2 or CS:GO. That makes sense to some extent since Dota 2 is free and CS:GO is often on sale and a lot of people like to Smurf. Anecdotally both of my CS:GO playing friends have smurf accounts.

Although this is a separate issue to the greater point that most people play one game. My bit of anecdata is that me and all of my friends might try out some flavor of the month game or something that caught our eye on sale, but those tend to be one-and-done playthroughs. However, each of us has a game that they play regularly that has an order of magnitude more hours on it than everything else.