This answer is pulled from the big breakdown of our marketing plan. 

Why are we not active on social media?

Currently, our social media work focuses on supporting our authors.

Eventually, we will have a social media presence for readers, but not for a while, given the limited value of these channels for a website like ours (we are very different from an author). We want to focus our finite resources on the highest-impact work, which is through channels like search and email marketing.

Social media has repeatedly screwed everyone who uses it (especially Facebook), and we won't invest in it until we have maxed out the higher-value channels. Social media does things like not showing your posts to but a small percentage of your followers and doing everything they can to force you to buy ads or boost posts.   

Why are email and search higher-value channels for us?

Readers using search to find a new book have a much higher value than readers browsing random stuff on social media. When someone searches for "books about space" or signs up to get book recommendations every two weeks, that strongly indicates they are looking to buy a book. Thus, that traffic is far more valuable than the random person who sees a post about books in their Facebook feed. 

Similarly, if we have an email relationship with a reader and they already trust our recommendations and brand, that makes a new book much easier to sell. 

We don't have the resources to take on every marketing channel, so I have to focus carefully and make sure each channel delivers the highest ROI for the website.