I don't know how HN feels about Stadia, so a honest question: why is it unpopular? I personally find it absolutely astounding that anyone can question that this
is the future.
I'm absolutely confident this is the future. Except, unlike you, I don't mean it in a positive way: I find it to be a one more face of the impending doom, anti-utopian authoritarian future, where people will be forbidden to perform arbitrary computations without a special permission. But that's that kind of wild socio-philosophical predictions that nobody discusses seriously, and nobody even thinks you are serious for suggesting something as preposterous (but then it happen anyway and nobody is really surprised).
On the technical matter, though, it is so much better than owning your own hardware, that it's hard to imagine how that could fail. I mean, obviously, Google will not succeed in making their own games (never could have). And of course current state of Stadia may not suit the "real gamer" (always a minority), because you can have a better performance on your own hardware.
But these problems will be solved, eventually. Better studios will make better games for this kind of platform, eventually it won't be games only, but the whole workspace. CAD running on Stadia will perform better than it could have on your upper-middle-range laptop you paid a shitload of money for, and that still lags and overheats when running your 100-tab browser on it. Your client device will be cheap, completely silent, low-temperature and will run on a battery for several days (that is, with no power-battery technology improvement). Light and portable. It will be unbreakable, compared to your current PC. Basically just a good display, a networking card, and some input device. There is absolutely no way your software won't run better on a shared hardware than you can buy for the same amount of money it will cost Google (or whoever will succeed with this).
I don't know if latency will ever be low enough for every human-use application (which again makes me wonder why are they starting with games: probably the most latency-sensitive thing an average customer uses), but it is surprisingly good right now, and there's still some room for improvement: computation servers will be more evenly distributed (CDN-style), and last-mile latency (the biggest problem, anyway) will improve in the upcoming years, especially on mobile.