Why Stadia instead of e.g. Geforce Now? You can play your existing purchased library via other streaming platforms, and you can switch to playing them locally if you ever buy a gaming PC without having to repurchase them. With Stadia you're locked in to having to buy your games again if you ever want to play on a different platform.
(not trying to criticize, just curious about the differences)
(not trying to criticize, just curious about the differences)