It’s totally something they can do, but it seems short-sighted. They had to know that this wouldn’t actually stop the momentum around OpenTF, but just result in HashiCorp giving up the control they have over the canonical namespace.
As precedent, Docker allows Kubernetes and Podman to access its registry, for example.
Is it short-sighed? If you think they will go down in market share from now on, yes. But Hashicorp probably thinks it won't or it wouldn't have made the change in the first place. For them, it's all the way up from here.
There same logic applies to users; at this point, I have to assume that the only reason that Hashicorp is providing anything to people who aren't actively giving them money is to try and get money from them later. This is also one of the reasons I'm abandoning them ASAP; now that the money squeeze has started, it's not like they're going to stop.
At some point third party and independent module and provider developers will need to decide whether to cross-support both tools.
I don’t think Hashi is going to go out of their way to make life easy for Terrafork. Cross-compatibility won’t last long.
So it _seems_ (the word I used above as well) from my perspective that they’re giving up a bunch of soft power for little gain, but it's very possible that I'm either wrong about the value of the soft power, or wrong about the cost of running the infra.
Don’t give them any ideas. Nothing would stop them, though it is probably hard to actually enforce on a public repo.
They do have a search interface, if one wanted to look for their favorite: https://gallery.ecr.aws/
Anybody should be, as is sensible in any case, mirroring in a local registry as minimum. Probably it's even better to investing capabilities to be able to build all the images you rely on for being able to apply security patches etc