Google is good at infrastructure but they're not uniquely so and all of their competitors are better at building platforms. They have competitors from both of the dominant console vendors, dominant cloud service, and nVidia. Whatever technological edge they believe they have is going to be a tough sell, especially since both AWS and Microsoft can match or exceed their cloud infrastructure and all three services are available to any publisher who wants to roll their own.
Something like Stadia requires customers to believe that it won't go away. Google, given their long history of mediocre commitment to projects, already had considerable skepticism for Stadia from Day 1. Shuttering their internal studios is just one more signal to skeptical customers that Google really doesn't know what they are doing and doesn't care.