And very easy to automate. We know they can do it. But until there is sufficient threat of action if they don't then they are happy to let their users get fleeced in exchange for the advertising $.

There is an argument that "if they crack down on the easy to detect stuff, the scams will just get more clever" but that is not at all why they aren't making more effort.

One funny thing I've noticed with facebook, is that if you start responding to such adverts with comments along the lines of "this is obviously a scam because..." responses, they start showing you more and more of that sort of scam presumably because you have shown engagement with the previous ones.