You seem to be using "non-gamer" as a synonym for "too inexperienced to use basic modern technology", which I don't think is a widespread problem outside of age ranges that didn't grow up with the internet. A much bigger group is surely just people that aren't that interested in video games. (Unless you think Stadia is actually going after the geriatric market, which seems short sighted.)
Too inexperienced to use technology is a strawman, the real comparison is do they prefer the benefit of the better UX more than they fear the amorphous dangers of lock-in. The answer is easily yes.
The problem isn’t just lock in. There are also less games on Stadia. The lack of available games is directly due to Google’s strategy of recreating yet another App Store.
Steam is free by the way, since I guess I didn’t point that out in my last post. You just have to buy the games, same as Stadia.