What I don't understand is how FB and Insta are just full of spam (from spammers, not Meta AI) now. It used to be that FB was the absolute best at getting rid of spam and now they appear to be overcome by it?

Because if you report something they do nothing about it. I have seen complete scams on there and they do nothing about it. At the same time the site wants to control your worldview so lose lose on both scores.