I think I understand how the federation system works currently and I'm not sure if I think this is a good thing, but why does federation require the entire link between communities to be broken?

Like say that Community A wants to block out Community B. That's fine, but can Community B still see posts on A? And if not, why not?

And to go further, if I'm part of Community A and I still want to interact with Community B, why can't I? Like is there a reason for forcing users to only interact with communities that are federated?

Again, I understand there are restrictions with data and how things currently work. I'm just asking from an abstract perspective about the fundamental ideas.