Pay closer attention to purchasing items on steam, they purposefully avoid using words like 'own' or even 'buy'. You 'Add to Cart' and 'Purchase' and when you buy something, it says: "Any digital items in this order are now registered to your account on Steam. To access your items, simply visit your library in Steam whenever you're ready." I felt like I owned it when I paid money for it and that's kind of the trick, but reading the wording definitely changes things.

On Steam's end, it was already decided long ago. I'd say a lot of it is contractual and Steam likely couldn't change it if they wanted to, but then they were also involved in drawing up the contracts.