I have a self hosted Forgejo instance with disabled user registration. The problem is as you mentioned ,- nobody wants to create yet another account. What’s more, it’s not possible to create PRs using e-mail.
I’d have to give out my e-mail somewhere on the git page then say “send patches here”.
It’s somewhat wise to disable user registration because users can freely fork your repos within your instance then change the fork to host whatever they want.