Granted, a lot of home PCs and gaming PCs are single-user environments. The “personal” computer. In that case there’s no reason games and applications can’t be installed in %LOCALAPPADATA%, and in fact, I think windows has an environment variable or registry setting for that.
I tried setting up my main windows gaming machine with a separate admin and user accounts, and tried to set it up to be multi-user. It didn’t work well. Most games worked but some random games had all sorts of bizarre issues, from only being able to run as admin, to requiring messing with directory permissions to just plain strange behavior but working sometimes. Steam also really didn’t like if I tried to run games as a different user and got very confused at times by the multiple user accounts