This never occurred to me, and considering my dissertation was on a The Secret Garden as a Gothic novel (an adult genre) and genre theory and the attitude of adults to children's books, I FAIL. Very interesting!

I wonder if it's the amount of collaboration in fandom generally - Big Bangs/Reverse Big Bangs being a good example, of course - that allows for more illustration as opposed to more general fanart.

I wish there were more illustrations in adults' books!