Call it out, and employ an n-strikes-process - after you’ve given a particular user a chance to get their act together, simply block them. Now they will no longer waste your time, and in time all you will have left are the users worth remaining connected to.
The problem is, people don’t look at Facebook as an experience they themselves ought to actively curate - it’s mostly out of obligation at this point. They feel guilty if they don’t remain connected to this relative or that friend of a friend or some celebrity or brand, and so they put up with whatever they’re spammed with, rather than choosing to improve their situation.