Why Are Books Perceived as "Literature" Unpopular?

In a recent post that can be found here, I mentioned that writing a book that can only be labeled as "literature" (as opposed to thriller,  detective story, romance novel or some other popular genre) is a kiss of death in the current milieu.

I mention that because in a letter to the editor published in the May 6, 2016 NYT  book review section, William F Wallace, of Brandon, Miss., concludes his missive as follows: "so readers don't buy too many books they suspect are 'literature.' Have you noticed that?"

Well, I'm sure The Times, along with the publishing industry has, indeed, noticed that.

Which begs the question "why don't people want to read such books?"