It has been nearly 10 years for me since I have used FB. I still communicate with those who I knew from Facebook, but not nearly as much (which is ok by me). Most users who have FB also have a phone - the same one they use for FB - so they can just as easily call or text. It boils down to ease of use. People can send a message on Facebook to friends and family and not have to respond like they would a phone call or text. This strongly suggests, to me anyhow, that people use FB because it is easy and their network is accessible on demand. If people could respond to text messages selectively without any argument from the peer who sent it, like they can on FB, here on Steemit - we would have 4 billion users too. Once there are enough people here to substantiate the need for users to be here in order to access their network - we will see a massive influx of new users.
How we get to this critical point is a balance of community engagement and reducing the learning curve necessary to use this 'futuristic' platform. It will come in time.