Earlier quoted context omitted.
Steam provides a CDN, updater, friends list/social infrastructure, really terrible but functional user generated content sharing infrastructure, and cloud saves to game developers, so it's pretty appealing even if you're a team inside Google since the alternative is building your own installer and updater - Google has no competitor to Steam on Windows or any other platform of note other than Android. Also, Gamers act…
To be more specific, gamers get annoyed when they have to install yet another "game manager" program to play a game. This is especially true when that game manager is well know to lack features and be insecure. Installing a game standalone doesn't annoy anyone I know (though, to be fair, I'm now older with few friends)
Every Ubisoft game since Black Flag that I've bought from Steam has required Uplay.
I'm sure there are other examples, but Steam isn't preventing users from being hit with another "game manager" download. In some cases, it facilitates it.