Why is the selection of games at Google Szadia on Android / Pc so small?

I bought the Stadia Pro subscription to play games like Red dead redemption 2, Hitman, Cyberpunk etc. On my Android device or PC. And on the Internet it is also said that you can play these games with Google Stadia. However, all of the games are not available on my Android device and PC. And the choice of games isn't that big. There are also videos on Youtube where people play these games on Android devices. Does anyone know why this is?

You still have to buy these games from stadia

Yes i want that. But you can't even see them in the store.

Google Stadia is an epoch-making flop