I enabled user accounts because I wanted people to be able to get notifications when someone responds to their comments. The problem is that I get tons of fake user accounts. I just cleaned out dozens of what appeared to be fake accounts.
Any user account that posted at least one approved comment was not deleted.
If a registered account has never posted a comment, I looked at the user name. If the user name was just random letters like this: OIYgboyugLJHglihg it got deleted.
If the user name is John.Smith and the email was Em.ily.John.Son@mailbab.com then it also probably got deleted.
If your account was deleted by mistake, my apologies. As you can see, the best way to have your account not get deleted is to post a comment (any comment) under that account. That way, I know you are a real person and not a spambot.