There is not much clarification due to there not being a reason as to why they closed your account. Are you sure they didn't send you other emails or notifications stating the exact reason? I'll have to assume that the country or state you live in is excluded for legal reasons, or you have somehow violated their terms of agreement, or you are underage. Mind telling what country you are from?

They at least don't suspect you from illegal activity, otherwise they wouldn't have allowed you to withdraw anything.