At this point sociala media has become a television, on twitter I just unfollowed everyone who have't followed back and I keep seeing the same antisemitic, antimuslim, anti-EU, anti-woman, anti-immigrant shit. My SO happens to see very similar posts to the point that I can't show her a funny post because she would have already seen it. There are some different posts of course but the money shot is mostly the same.
They probably show posts based on location and background, so essentially just like Fox, CNN, MSNBC but everyone sees theirs from the same screen with the same agenda pushed from all of them.