Read the EULA sometime on a game you "own" on steam (or any platform for that matter).

Almost without a doubt you're being granted a license to one copy of the game used the way they say it can be used. Most of the licenses are revokable for violating the conditions, many just outright say "hey we can take this away at any time for any reason and you can suck it" which is in a legal gray area I suppose.

As far as how it's legal, you don't have to do business with any of these various entities and you're agreeing to their terms when you get their product. Plus, like you said, there is very little consumer protections in place.

I agree we need more consumer protections on general and particularly for digital purchases. However, at least in the USA, the prevailing political winds are heavily in favor of companies and anti consumer. The Trump admin basically dismantled the bureau of consumer protection so ... That should tell you their priorities.