Actually, in many nations, they're legally required to give you the option to have all your data deleted within a reasonable time frame. There is a recognized "right to be forgotten" in the EU and some other nations. The US there are similar laws in several states. Though you may not live where there is such legal protection, Facebook operates where those protections exist, so they necessarily have the mechanisms and procedures in place to actually delete your data. You just have to go through the right channels to make that happen. It won't happen just because you close your account.
The best way to delete your account was to delete it like I did, in 2010, roughly 1 year after I created it. I realized very quickly what they were doing and I knew it was beyond dangerous. This was not Friendster and MySpace, this was monstrous and pure shit. I've been railing against it (on accounts that require no identifying information) for the better part of 15 years now.
Fuck all of them and any sites like them. If you're still a member, then you must accept some blame, you know it's shit and with a tiny bit of extra effort you could just email your friends and family to stay in touch.
Oh, man, I would have to figure out how to log in to my Facebook account first. That'll take a team of archaeologists and a squad of 90s hackers tag-teaming a single keyboard, at the very least.
Now, if you find a way to get the rest of the country to stop using Whatsapp so I don't have to go live as a hermit, that's a boycott I could consider.