I'd say the biggest effect was that consumers didn't trust Google to actually keep their purchases alive for more than two years. Techwise Stadia was actually very good and it could have been a good alternative to a full-blown gaming PC for people who are not gaming enthusiasts.
Google should have launched a new PC game store that lets you download your games. For a nominal monthly fee, you can stream those games from Google's servers instead of needing to buy expensive gaming hardware.
This would have given enthusiasts a lot less to hate about Stadia. It would have given customers a lot more confidence in the long-term viability of their purchases. It would have highlighted the flexibility offered by Google's streaming platform without making putting up with its drawbacks a requirement to enjoy your games. A player could start out only streaming their games, then upgrade to a real PC down the road to get an even better gameplay experience out of their existing library.
For many enthusiasts, the product Google actually launched felt like an existential threat to their hobby. They feared games could go streaming exclusive. Publishers could use it as a form of extra draconian DRM, or start designing their games around the limitations of streaming. As a result this turned many of the biggest gaming enthusiasts, the people casual players will often ask for advice on what to buy, into ant-Stadia evangelists.
"Google should have launched a new PC game store that lets you download your games. For a nominal monthly fee, you can stream those games from Google's servers instead of needing to buy expensive gaming hardware."
Nvidia already has a product like that called Geforce Now. Instead of having it's own store it integrates with Steam and GOG.
There's still the problem that is a hypothetical customer wants to game enough to pay for Stadia but doesn't have the funds for a gaming PC... why don't they just buy the $300 dollar Xbox Series S?
