It's most likely because you got a warning about not using your real name, If you don't change it, it gets deleted

Nope. No warning, whatsoever

Facebook banned me with a message sent to my Facebook page and email.
It was for frequent inactivity. One check for being gone for a whole year (12 months). Temporary week ban.
Another, which was a perma-ban, because I was gone for a single season (4 months). Because of the past ban, this was perm.
Facebook is evil. I used my real name and only real info! And now my profile will exist forever there without me doing any updating with it!!!

man what a good lookin rai

Yet another reason hate this planet. :B

I remember when I got banned from Weasyl- they exaggerated everything. :U While I've never been banned from Facebook (they once deleted my account on accident, but I got it back), I know how jumping right to account deletion without even a warning sucks some serious ass. ~_~