2) PC gamers are on average very particular about frame rate, quality, and lag and these things weren't great with Stadia.
3) The convenience of not being tied to a specific device was nice but for both #1 & #2 above the convenience came nowhere close to overcoming the biggest flaw: lack of library portability. I certainly wasn't willing to repurchase games on Stadia. We see this in reverse with Stadia users about to loose everything they purchased.
If Google really wanted to do something in this space they'd repurpose the cloud GPU resources dedicated to it towards compute instances w/ Windows and/or a partnership with SteamOS that would allow users to install whatever they wanted: Epic, GOG, Steam, etc. Leave it up to the user. And leverage their streaming technology for the same convenience Stadia had provided, complete with love streaming to YouTube Twitch etc. Niche services like this exist but they're expensive. Google's scale would help solve that.
Of course even that game may be lost with the arrival of the Steam Deck. I can play nearly every game I've tried in it, including many unsupported, and the experience is great. In a hotel I can connect it to a TV, or I can stream it to a larger screened but low end laptop right next to me, and many games play perfectly well even on the small screen. The advent of relatively inexpensive portable hardware like this may in another year or two render the cloud streaming game concept completely moot.