Having games working flawlessly, and not having to purchase the hardware, and do long downloads and installs is quite useful, especially for casual gamers.
> Stadia has a worse selection of games
Give it (or some alternative gaming service) more time.
So far Valve is doing good. But in the long term, it is dead end.
If you're a casual gamer you don't care about high end 3d graphics which completely eliminates the need for Stadia.
Stadia has a worse selection of games than even just native Linux and Proton lets you play most Windows games which has an even bigger selection.