AWS probably doesn't care much for it being closed either. But the benefit of being open is that folks can investigate, report and fix bugs. For example, at Spacelift we found a fascinating corner case where an RDS DB could be dropped if the call to get its details resulted in a transient API error. We wouldn't be able to do it if the code wasn't open. I also believe that the AWS provider in particular gets quite a bit of attention from the community outside Hashi and AWS.

All the providers are still MPL licensed, however. Maybe I'm missing something, but what part of the license change for Terraform core prevents someone from investigating and fixing a bug in the AWS provider in a similar manner going forward?

Even Terraform core remains source available and so 'community' users can still take a look at the source code and identify/report/fix errors.

Oh, the core license change is irrelevant here, and the providers are MPL.

I was just responding to a comment on how AWS didn't care if the provider was open. IMO there's value for them in it being open.