Because in this case the relays "decision" to ban them is based on the arbitrary actions of other users. There is a difference in a relay having arbitrary rules (such as "no using the word avocado on this relay") vs. a relay allowing the arbitrary actions of other users to dictate what/who is and isn't allowable. Maybe there is some more specialized use case for such a relay, and so I don't think it shouldn't be tried. But I don't think it is a good idea just for general use.