An even better question is how many people lose interest in checking Facebook every day because their feed is filled with baloney.
Its a lot like email. The email address that only my friends have, I watch all day. The email address every asshole I've done business with in the past 5 years has I check about once a week. (Everyone important has my phone number.)
If your feed is filled with baloney, and you let it stay that way, then it's partially your fault as well. Facebook has so many ways to control what shows up in your feed, and you should really take advantage of them.
Don't like updates from a specific game or app? You can turn off all updates from that source.
Don't like updates from your uncle grandpa joe but can't deal with the social fallout of unfriending him? You can change your subscription to only see "important updates", or you can unsubscribe from a user altogether.
Friended or subscribing to someone cool and don't see enough of their updates by default? You can specifically subscribe to see all of their posts rather than just the ones Facebook thinks you'll like.
There's even more options than that available to you, just click on a post and choose Hide, and you'll get multiple options for what you can do with that. Use it liberally if your friends list is full of people who post things you don't want to see. The power is in your hands.
It's not that easy to filter, for example I want to keep in touch with my smaller cousins, and I like seeing family photos, but I don't want to see more One Direction or Justin Bieber pictures.
I can either block every photo or none, but there's no "block Justin Bieber and Zayn Malik photos" filter.
Edit: that said, I find Facebook extremely useful for keeping in touch with my family, which is spread all over the world (from here in Uruguay to the U.S. to Europe to the United Arab Emirates).
As a side note, I use the Unbaby.Me extension for Chrome, and it does a good job of keeping unwanted pictures out of my feed based on what is mentioned in the text of the post. It could easily be configured to also take care of justin bieber pictures.
Its a lot like email. The email address that only my friends have, I watch all day. The email address every asshole I've done business with in the past 5 years has I check about once a week. (Everyone important has my phone number.)