Because Facebook used to be a place where you could go to see status updates from friends/family in chronological order. People posted what they were up to, and people left comments. Things were simple, and great.
But then Facebook decided they needed to make some money. So they started allowing advertisers to inject things into your feed. They often tried to hide it in the form of "things liked by a friend of a friend", but it was still obvious.
To make even more money, Facebook decided to do away with the pure chronological feed, and they replaced it with something much more vague. The vagueness of it all made it all that much easier for them to inject "recommended" content that they were getting paid to show to you.
Nowadays, Facebook is completely unrecognizable. The vast majority of a typical Facebook feed is nothing more than memes, ads, and the equivalent of shitty email forwards. Scattered throughout the noise are just enough tidbits of things you actually want to see, from friends and family. Just enough to keep you hooked.
People put up with it, but a sort of deep resentment has started to take hold. A lot of people are sick of being farmed by ad companies. They are tired of being a product. They are tired of seeing nothing but ads and stupid, tired memes. They long for the content and direct connection that made Facebook popular, but alas, it is never coming back. That kind of content doesn't make money for Facebook.