Anytime I open the Meta forum I see this:
At least 5-6 sometimes 10 threads in the top 30 where members are asking why they are banned and how can they be unbanned.
It has been suggested many times and this could be sorted out by changing the message that the users receive when they get banned and adding to it that the ban is Permanent for plagiarising, since that is the most common reason. The ban will not be lifted and it will remain permanent! That would take care of at least half of the 'Why is my account banned' threads here.