The point you might be missing is that a provider who is banned/delisted might actually be a good provider!  There are many good providers who have asked to be removed from the database (delisted) for various reasons.

There may also be some ladies who are good providers, but just can't follow the rules - posting false reviews, spamming the TER mail system, etc. so they go them selves banned.

Also, another point I will make is that if a provider is a rip-off, TER will not pull their reviews if asked to do so (i.e. become delisted).

It's not so black and white.....