The reasons are multiple :
- Facebook's visibity limitations : Say you create a page about your niche, you have to put ads out there to reach your audience and get them to like your page. Now even if you only purchase ads from Facebook you will still get clicks from click-farms as demonstrated by Veritasium in this amazing video :
- given that some of your fans aren't authentic, they won't engage with your content at all, hence Facebook forcing you to purchase ads to reach YOUR audience that has already shown their interest in you by following your page. It's like opening a bakery, engaging with people and becoming friends with them, and everyday you'd have to go find them and tell them about your bakery again.
- Facebook's limited engagement: Facebook has a CTR of 0.05%, compared to YouTube that has 2%, it's just nothing. Because when people go on YouTube, they're willing to spend some minutes watching things, but when they go on Facebook they almost already know what they want to do "See notifications, talk to a friend, respond to an event, upload a picture..." That's it. They are legitimately unwilling to interact with ads.
- Facebook's definition of "engagement": I personally have seen many posts on Facebook that I liked, without actually clicking the like button, but if my fans do the same with the posts I make, facebook will restrict my reachable audience thinking that my posts are not engagement-worthy. I don't always want to post some sort of a question to get people to answer and engage with me, sometimes I only want to post pictures, no need for anyone to "explicitly" showing that they "CLICK-LIKE" that picture for Facebook to count it as an engagement.
- On NASDAQ Facebok is always red (-0.49% today, VS. +0.22% for Twitter).