I think almost permanent bans are caused by plagiarized behaviors. And if they are banned and receive announcement without any reasons, they should accept it because this decision is carefully considered by mods.
Mods make mistakes too. There is nothing wrong with genuine appeals. Unfortunately most of the appeals in Meta seem to be coming from shitposters who know exactly what they've done and/or don't think that rules apply to them. So even though it wouldn't hurt to have the ban message show the reason, it would probably not reduce the appeals. Keep in mind that only ~1-2% of permabanned users try to appeal.