It's a big gamble to port a game to Stadia, and risk customers being mad at you, when Google inevitably pulls the plug
people who aren’t serious enough to buy a gaming PC or a console but still want to play a games occasionally.
People who want to keep their lives simpler by converging to fewer devices
I am sure there are many more
Doesn't matter how flashy Stadia is, you're hardly going to get past the loading screen on AC Odessey/whatever before you run out of time.
Put another way: if Stadia has the games you want (big if now, but improving over time) why shell out for a console?