I take a facebook "sabbatical" every couple of years where I delete my account completely and permanently, and then come back with a brand new account a few months later. It irritates my friends but I love it.
Why do I do it at all? Being off Facebook is good for my mental health-- this is the main reason. Privacy reasons are secondary but also important. I've posted some really stupid stuff in 2004 that I'm glad is (theoretically!) stricken from the record.
"When you delete your account, people won't be able to see it on Facebook. It may take up to 90 days from the beginning of the deletion process to delete all of the things you've posted, like your photos, status updates or other data stored in backup systems. While we are deleting this information, it is inaccessible to other people using Facebook."
From a Facebook-makes-money-from-retaining-user-data perspective, I would imagine they are making every effort to ensure they're permanently deleting user data only where legally compelled to do so.
In effect, what the GP does in no way helps provide more privacy from FB for the GP.
It's interesting to me that my friends ask did you see my X post on FB instead of telling me about things in their life.
Do you have some evidence for this or just presuming?