I think about this a lot. As a new parent, it's been very apparent to me the incredible craft with which certain picture books are made with, and what a subtle art it is too, such that many children's authors and virtually all publishers seem utterly oblivious to what that craft is or looks like.
when I think about them I wonder: are picture books secretly the ultimate medium? they combine writing & illustration but they're ultimately about performance. they're about the most profound things but also need to connect directly. they're designed to be read again and again, on a daily basis.