Login to Steam. Go to your profile page, look for "Games Owned"

That is a lie. What it should say is "Licenses Owned".

Their EULA, and any additional you agree to as part of the purchase process make it clear (some do it better than others) that you do NOT own the game. You have a license to play it, and that license can be revoked.

Battle.net, Origin and others have the same.

They can take anything away.