If it is possible to play Stadia games in Standard Definition video resolutions like 360P and 480P, I think many people with slower internet speeds, and bandwidth download limits may more likely play games in non-HD resolution, so they don't have as much slowdown problems, and reach their bandwidth cap.
I guess Google Stadia may have an Auto-video resolution where Stadia may lower the video resolution to 480P or lower when you use Stadia on a slower connection, or Stadia is being used on an older 480P LCD TV or a tube TV which is 480i.
Hopefully it’s not like Remote Play on PlayStation where, if you have slow internet, it drops to the quality of 10 year old blocky YouTube videos, and then the frame rate stutters and gets choppy. Basically becomes unplayable.
I think there are still a lot of people with older wireless routers and subscribe to slower wireless smartphone plans which may have problems streaming games and videos in 720P, 1080P, and 4K, so 480P would be their only choice.
Playing games in 480P is similar to watching a DVD movie which video is encoded in 480P. I played many Playstation 2 games which are 480P quality, and they look good for the time.
Some gamers who mainly play web browser games like Facebook games, Runescape, and flash games maybe fine with 480P quality games which may look better than most web browser games like Runescape.