On middlebrow books

What should I make of the fact that middlebrow nonfiction tends to be so much more rewarding (for me) than middlebrow fiction?

Candidate reactions:

1. What distinguishes highbrow from middlebrow offers much greater rewards in fiction than in nonfiction, for intrinsic reasons. Most obviously, the bare transmission of information matters a lot more in nonfiction.
2. What distinguishes highbrow from middlebrow offers much greater rewards in fiction than in nonfiction, because of how highbrow nonfiction and fiction are generated. (Should I really read recent journal articles about Abraham Lincoln instead of Abe?)
3. If you read something wonderful, it's easy to classify it as "middlebrow" if it's fiction but tempting to elevate it to "highbrow" if it's fiction. (If A Moveable Feast weren't so wonderful, I'd probably not be tempted to think of it as highbrow.)
4. I'm deceived by a short-term trend. (A few years ago I read The Dog, Straight Man, and Dear Committee Members and am very glad I did so.)
5. I'm worse at selecting middlebrow fiction.
6. The comparative advantage of books is greater for middlebrow nonfiction than for middlebrow fiction (television and Twitter exist!).

P.S.: The impetus here is The Startup Wife. It tells a basically plausible and engaging story of a business; it's funny; the writing is crisp; and it's well-paced. I devoured it. It's not always easy to make sense of the book's politics, but what matters most for its plot and aesthetic agenda--sexism, gender dynamics, and so on--seemed on point to me. But despite its being the very best middlebrow fiction book I've read in years, I'm only somewhat glad I read it instead of the next thing on my list.