I've talked about this somewhere else. What you're seeing is just a manifestation of what I call "the fundamental problem of user created content." Said problem is that warehousing and distributing content scales insanely well but curation does not. Until we have strong AI, curation is a manual process. Moderators just aren't efficient enough at processing content for their output to pay for a full time salary. You can cut costs by making end users into moderators (the Reddit model) but results may vary.

This problem applies to other forms of sites and content as well. The app store gets hundreds of submissions in the game category per day. Hosting and distributing that content is easy. Only a tiny fraction of those games are going to be played and rated enough times to show up in a recommendation engine. The bulk of the incoming content stream isn't being matched to interested people at all (sorting by interesting is the same curation issue as filtering by offensive).

Literally every content platform is going to have some problem similar to Facebook. We can blame Facebook, but the reality is no one has a good solution. Not even me.