I think Stadia is THE example why an all streaming gaming platform doesn't work from the ground up. Paying Google money to lease a server and paying each publisher money to stream titles is frankly stupid and more expensive then buying a console and games. Just paying for Stadia and buying the games might be an uncertain investment with Google's reputation and in time, a Stadia subscription is not financially more interesting then buying a console.
Sony and Microsoft's streaming services are different, since they can tap into a much larger library of games and already have a lot of contact and leverage over publishers.
Streaming will prove to be just another option next to digital and physical games. Just as the balkanization of video streaming platforms might make buying discs more interesting again.