I've been studying this fairly in depth and it's my belief that the main reasons writers do that is because social media is designed poorly.

It doesn't actually show your content to most of your audience. So most people don't see everything, they might see 1 post of 7.

If we could guarantee deliver of our messages, the volume wouldn't be nearly as necessary. I've been building around that philosophy. I think the right toolkit makes it much easier to have your work read. Happy to chat if you're ever interested: https://twitter.com/leo_guinan