Smartphones and tablets have been a platform that has dominated every aspect of our life. The only area that it has been lacking in is in Triple-A games. Tons of people have always asked "damn, wouldn't it be sick as fuck to play Destiny 2 on this road trip, or waiting for my flight?" I happen to be one of those people! I travel frequently, and Stadia would be right up my avenue. I was even in the alpha tests last year and it was incredible to play AC via my browser.
So it makes sense for Google to want to target those consumers, because there are millions of them. And there is probably even more in the south east asian countries where owning hardware for your games doesn't really make sense, because, for example in South Korea, most people who play games go to a gaming cafe and sign in for a few hours and that's how they do it. Stadia introduces another avenue for people to play those games without having to buy an Xbox One or PS4 or PC.
And the million dollar question is - what happens if Stadia fails?
Google will probably collect so much data from Stadia that it will not matter if it fails and they have to close it down. Either way, they profit off of this project.
I also found this tweet interesting, given that many people say there is no interest or marketing for Stadia.