I think the key here is engagement is based a lot on content quantity, not quality. If your feed doesn't have a lot of natural quantity associated with it then FB will find something to stuff in there. The reality is that most people don't have a lot of quantity on their feeds from their friends so that means they get the AI slop to fill the void. At least that is my complete guess on a root cause of (some) of the FB slop. I haven't logged in for 6 months and I am now checking it 1-2 times a year because the last few times I logged on it was pushing hate content at me.