The Facebook game has some very clear rules. And though they might change the rules a little bit here and there (underwater level, anyone?), the logic behind those rules stays essentially the same.
Learning the rules of the Facebook game
Remember: Facebook is a for-profit corporation. Facebook’s objective is to get people to visit Facebook more often and to make each of those visits last longer because more time on Facebook means that person gets exposed to more ads. More advertising means more money for Facebook. No matter what else they do, this is always true. To achieve this they try to show people content that will evoke strong emotional responses from them; ideally, positive emotions, but they’ll take negative emotions too if it keeps those people on Facebook longer!
When using Facebook, you are almost never shown every post that your friends make. Instead, things that Facebook think will engage you are made very obvious to you, and things that Facebook thinks will frustrate you are hidden from view. By tracking what you “react” to (through the iconic like button, or its newer compatriots such as love, anger, sadness, etc.), which posts you read the entirety of and which you scroll past, what links or ads you click on, and what sort of topics you post about, Facebook’s algorithm learns detailed information about what interests you and then tries to show you more of that type of thing. If you always like pictures of cats when they go by in your feed, you’ll soon find that you see more pictures of cats. If you hide posts about a particular political party you dislike, you will naturally be shown fewer and fewer posts about that political situation or party.