If you want to make a cloud gaming service that isn't expensive and a good experience, you need it to be huge scale because more locations is essential for less latency, and you need a varied workload instead of just people playing games to amortize the costs of the servers. I don't know what other stuff Nvidia or Valve does that would keep these machines productively busy during the work day, but the big cloud companies probably have all kinds of things to justify over-provisioning machines so it seems like they have a limitless supply at peak gaming times while being cost-effective

I think Amazon, Google, and Microsoft will dominate cloud gaming eventually.