My guess is money. Facebook has such a MASSIVE user base. And people are getting accounts stolen a LOT, from either social engineering or password reuse. But

My guess is money. Facebook has such a MASSIVE user base. And people are getting accounts stolen a LOT, from either social engineering or password reuse. But there's also a ton of people knowingly breaking rules, getting banned, and then trying to cry that their account was hacked. Trying to differentiate between someone's account being taken over and abused versus someone just simply being abusive and lying about it to support costs a lot of time, and time is money. And with the scale of Facebook, that adds up to a LOT of money. You have to train a large staff to understand social engineering and be able to tell the difference between someone who actually can't figure out how to log in, versus a jealous ex who is trying to social engineer their way into someone else's account. It's a lot cheaper to just let the bans stick, even if it loses a few customers.