I think the answer's obvious. Because they designed the product backward. They didn't think "what do people want?", or even go Apple and think "what COULD people want, if we showed them why they wanted it?".
When I think about Stadia, I *want* to be afraid. I want to see it as one spike (with Apple Arcade) of an encroaching change that ends general computing and brings game creation under a publisher system.
They pitched to the high-end hardcore gamer crowd, pixel shaders and AAA content. The exact people most likely to complain about latency. And they aren't obviously cheaper or better looking than the existing products.