Yes, this was a core architectural requirement of Stadia (running the games on Linux), as opposed to hosting virtualized Windows machines (which would've allowed serving up Windows-based games).
Whether this specific design choice alone killed Stadia, no one can say -- but it was probably one of the most important factors in its demise.
For me, the two most important aspects were: 1) it's made by Google so it will probably be shut down soon, and 2) if you already have any hardware which can play games, Stadia is strictly more expensive than buying and playing games locally. That's before I even got to the point of considering the size of its game library or the technical qualities of the service.
I play all my games on Linux, and in general, there are extremely few games I haven't gotten to run. Many just work out of the box through Proton, games not on Steam usually work out of the box with Lutris. This suggests to me that the Linux thing wasn't necessarily a big issue, if Google was willing to put in some work to get existing Windows games to work. AFAIK, they didn't do this and instead required games to run natively on Linux, which would significantly reduce the size of their games library (after all, why would a company invest time into porting their games to a Google product that's going to be shut down?).
Whether the US is even a market that's ready for game streaming is another question. Are there enough people with a high quality, low latency Internet connection that's close enough to a Stadia data center, who are interested in playing demanding games, but don't have the money for hardware yet can afford a monthly subscription on top of a high per-game price? Maybe it would be interesting if it worked like other subscription services and the subscription itself gave you access to games. I think Spotify would have flopped if you had to buy albums at their retail price in addition to the monthly subscription.
Likely it was caused by your computer and browser not playing nice with x265 hardware decoding, I used to run the gamelet on the same network as my desktop and would get the same on some configurations.
Frustratingly, it was not easy to know at a glance that this was what was happening, but there were times (many times, actually) where my chromecast ultra at home was performing much better with Stadia than my gaming PC
I got the same when I was running Stadia on a 2.4 GHz wifi network. Once I switched to a wired connection, it worked like a charm. 5 GHz supposedly works as well, but my robot vacuum cleaner needs a 2.4 GHz network facepalm.
I have a PV inverter which doesn't work if there's more than one AP with the same SSID and is 2.4GHz only... ended up buying an el-cheapo AP and giving it a unique name. PITA
Whether this specific design choice alone killed Stadia, no one can say -- but it was probably one of the most important factors in its demise.