Comment by mmooss

> There is just more of everything

If that was the cause, 1) book sales would drop overall, and 2) nonfiction books would perform the same as fiction books. The OP says neither are true:

"What has happened in the last ten years is that the overall industry has grown modestly, but fiction and nonfiction have basically flipped positions. In 2015, 6 of the top 25 bestselling hardcover books—this is a not-perfect but useful proxy for new books published—were fiction. In 2025, 18 of the top 25 hardcover books were fiction, meaning only 7 were nonfiction, almost an exact inversion of ten years ago."

They suggest some explanation:

fiction/nonfiction reading habits are extremely gendered, with 80% of women making up the fiction market, and nonfiction being a more 50-50 proposition.

and

Proportionally we are gaining many more women as readers and losing our few men.

EDIT: But they add: "The collapse of nonfiction is less a “male reading crisis” than a massive breakdown in the social fabric of trusting education, expertise, or any authority other than follower count and force of personality."