I might be wrong about this as I've not used Facebook for many years now, but doesn't Facebook require a phone number for new accounts nowadays, and requires you to use your real name as well?
Think of how many accounts are created for games reasons. Some games require friends taking action to progress. Some allow friends to send prizes like lives/money/resource.
Could be like my grandma who would occasionally manually log out of the app, but then the next time she loaded the app, rather than actually logging in again, she'd create a new account because that's what she did the first time she loaded the app and thought she had to do that every time.