I remember Google was talking up how you'd be able to watch a game stream on YouTube, then with a single click "fork" the game into your own instance and continue playing. Or even just basic things like watching a game trailer and being able to jump into a playable demo. But they didn't realize any of that, instead they went with the most conservative possible approach of selling games for $60, which is a non-starter in a world of constant sales and where Game Pass already exists. It's like if YouTube was a platform where every video was $1 to watch, how successful would that have been?
I also think if Google shuts down Stadia instead of pivoting into a Game Pass like service, the reputational damage to GCP alone will be more than whatever the cost of Stadia is.