they can login on a different instance with the same credentials.

Hey that’s me. for a long time I thought I could do that, and when I found out I couldn’t, I thought that meant I have to register to instances I want to interact with.

I think the biggest hurdle to overcome with threadiverse / forumverse is staying in your instance view/reader to continue interacting. There are Apps and front ends that help with that, but on web browsers but that’s yet another layer of quirks added onto new users to wrap their mind around