> If the controller is indeed "dumb" (just sending inputs), why wouldn't there be compatibility with Xbox or PS4 controllers?
The controller is not dumb, it connects to Google.
Also, as I understood it other "supported" controllers can be used (per https://youtu.be/k-BbW6zAjL0?t=683) but then you need to use another device/platform that does the connect-to-Google part, e.g. Chrome on PC.
edit: http://stadia.com/faq says USB HID controllers are supported on Chrome and mobile.
The controller is not dumb, it connects to Google.
Also, as I understood it other "supported" controllers can be used (per https://youtu.be/k-BbW6zAjL0?t=683) but then you need to use another device/platform that does the connect-to-Google part, e.g. Chrome on PC.
edit: http://stadia.com/faq says USB HID controllers are supported on Chrome and mobile.
edit 2: and https://support.google.com/stadia/answer/9338852 explicitly says PS4 and Xbox One controllers are supported.