There are a lot of posts & questions & other things in various places online wherein people are complaining about this happening to them. Usually there's someone to tell them that nope, it's something you did. I can guarantee that it is not, in fact, necessarily something you have done. Because it happened to me (which totally changed my opinion about Facebook being an awful company), and I went to specific lengths to ensure that Facebook would not reactivate my account when I deactivated it. Specifically:
- I did not sign in from any other devices. I do not have the Facebook app on any of my phones, and never have. Only two things have accessed it: my desktop computer and my laptop. After deactivating my account, I cleared the cookies on my laptop to be sure.
- I do not have any apps that could have reactivated it, because there are NO apps connected to my account.
- It is entirely implausible that anyone could have logged into my account with my credentials. My password is extremely long and complex (it is "hunter2"). In the unlikely event that someone guessed a 28-character password, they decided to...do absolutely nothing with my account. But I'll reiterate, nobody guessed my password.
- From what I have read, according to some rando on Quora, there is a "This is temporary, I will get back soon" checkbox?! Hmm... I'm not actually saying this is impossible. But when I deactivated my account I specifically checked for sneaky things like this because Facebook is an awful company staffed with terrible people, and if I trust them with anything it is that they will reliably do whatever thing gives nice values on the "Engagement" axis on a graph.
So...either Facebook does in fact randomly reactivate your account, or Facebook is doing some sneaky shit in which you have "agreed" to randomly reactivate your account. They are either betraying you, or they are using dark patterns during account deactivation such that someone who is actively looking for dark patterns is tricked into "agreeing" that they will reactivate it. Either way, it is being reactivated without your consent. Anyone that tells you otherwise is gaslighting you.