Why are many children’s book illustrators unwilling to work with self-publishing authors?

I am afraid, a few illustrators have very good reasons for this attitude. As a professional illustrator, I get emails from self-publishing authors all the time, who love my illustrations and want me to illustrate their book. They want me to quote a price by return email. But they don’t tell me if it’s a picture book, chapter book or middle grade or how many illustrated pages they need. Occasionally an author will say I don’t need a big fancy book, I only want a small book, maybe 12 pages. How much will that be? These questions put me in an awkward position. I don’t have enough information to give them a price.

They want me to just “sketch-up” something fast. “Don’t spend any time.” But they want the main character to look like their niece at four years wearing the dress…