Poster must be a PC gamer who doesn't use the Microsoft store (like most PC users who'd identify as gamers, probably?). It hit Steam this year, was on XBone and MS Store in 2018.
Personally, I'd forgotten there was a MS store until I looked this up just now.
And lord was it annoying as fuck to get off Microsoft store. It was something like a 50gb download and it could get version desync, the only way to get around was (in my experience) was to completely wipe it and reinstall. But completely wiping was ALSO super hard to do, because it was saved in like... $APPdata or some weird hidden folder.
All this on top of the fact that my c:/ drive is tiny and I want to install my games on an external harddrive. In fact I think I had a double install going at one point.
I'm glad I've avoided it so far. I already have three stores I use and that's at least one too many, but Epic won't stop showering me with free games (I've bought one and have a library of... 30ish? Maybe more?) so I keep them around for now.
I would certainly find it mysterious and confusing to find a game installed to %APPDATA%, and I've been a PC gamer for over two decades. Saved games and config files, sure, possibly mods too, but if a game installed somewhere without asking first I'd expect it to be in %PROGRAMFILES% or %PROGRAMFILES(X86)%. Either way, as the owner of a PC with multiple SSDs I'd be somewhat miffed by not being asked first where the game should be installed, as I put most of my games on my D: drive, which is much larger (but slower) than my C: drive.
Personally, I'd forgotten there was a MS store until I looked this up just now.