I dont think the GM's or BB-staff sit down and have a meeting, and look at a guy's nickname and go 'u know what, i dont like this guy's nickname, lets ban him".
its not subjective. The reasons for getting banned are pretty straight forward, unless you can justify it - but very rarely are you going to be able to justify it, so its not like the GM's are making a subjective decision. u break the rules, here are the consequences.
one advtange of not having transparancy is that it means people fully know why a person has been banned and therefore, have less information in forming ways to get around being banned. If you published a guy who was banned for multi-accounting and you knew that he had done XYZ to do that, then you would then be able to use that informaiton to form other ways of breaking the rules.
but if you dont know that that was the reason behind the ban, then its impossible to know whether or not his tactic worked. so in actual fact, having no transparancy can be a good thing to help prevent cheating.