elrac
I saw a free preview screening of Mission to Mars right before it came out. That horrible movie ended and the theater was dead silent, then someone yelled out, “I didn’t have to pay to see that pile of crap”. Everyone applauded.
She’s not your buddy, pal
I think there are a couple of reasons to not allow mods on one instance to moderate posts on another instance.
One example I can think of, if I wanted to grief a community I might go to another instance that doesn’t have that community, create it, making myself a mod in the process. Then I would request federation with the community I want to grief. Then I’d mod away all their posts, or do anything else I wanted. With some luck and okay timing I bet a person could do a lot of damage before federation was turned off. People in IRC chat rooms used to use a similar technique to steal OP from others in rooms. Making modding of federated content only effect the local instance would contain any of that damage. As a feature creep sort of feature, perhaps modding done on an instance could send a suggested mod response to the originating instance, and they could do what they wanted with the information.
Also, having it set up like I originally suggested could allow for other non standard federation arrangements. Like one instance that allows nsfw content in a community to be federated with one that auto blocks anything marked nsfw. Maybe even one way federation, where an instance shows posts from another in a community, but it isn’t reciprocated. I don’t think that would be usually the best idea, but it might work.