The situation is quite interesting here. - Imagine, you're living outside of USA/UK/Europe. - Formally, it's possible to proceed with "Permanently delete my account". - You will even receive email assuring you that two weeks later profile would be completely deleted. - Then, couple years later you'll occasionally seen email from facebook that someone tried to log in into your ("permanently deleted") account. - You'll…
In a very real sense, "you" still exist in Facebook. That's why when, weeks, months, or years later, when you login, Facebook recognizes you. You create a new "account", and Facebook very conveniently associates everything it knows about you (which it never forgot) with your new account.