I was having a hard time finding the statement that SpatialOS can't run apart from Google Cloud, but they do not allow self-hosting, meaning you are tied to wherever they put their servers which is Google according to the parent's source.

I suspect Hadean is similar, they've listed Microsoft as a partner, and presumably it's a cloud service that they are offering, so wherever they host it is where you get it, you're never directly dealing with the cloud provider or it's billing.

It's plausible, arguably, that both could shift to alternate cloud providers if they wanted, but I get them impression their customers have no choice in the matter.

Also, they do get a little further into the weeds, but it's hidden behind a hamburger menu: https://www.hadean.com/developer/how-to-get-started-with-aet... though a code example without access to the library or cloud service isn't a whole lot of use for testing out!