Such a good thread. A tangent from this, of sorts: https://twitter.com/malindalo/status/1250479301935464448
I think people look at "commercial" as meaning "books that will sell well," when that is clearly not the case--if publishers knew what was going to sell (especially at the point of acquisition), we'd all be much richer.
"Commercial" books seen as having the largest *possible* reach, things that are thought to have the biggest possible upside.
This is why "commercial" books tend to follow formulas or trends, the reading level is typically lower, the subject matter (perceived) as universal.
But just because they have the possibility for a large upside doesn't mean they'll succeed. The market is fickle, and people make their buying choices.
What's been changing in children's books is where people see that reach and upside. Whereas there was a time where non-white, non-cis, non-het characters were seen as not having a lot of upside, external forces have pushed publishers to recognize the appetite for these stories.
This is why what is seen as "commercial" can change. It's about the perceptions of publishers, what they can imagine for a book.
Anyway, random musings from my isolation brain.