Why Doesn't Fiction Have Illustrations with the Text.

Why doesn't grown up fiction have illustrations with the text?

The Island of Adventure by Enid Blyton, illustrated by Tony Soper,
one of my favourite childhood reads.

Well really and truly I know the answer. It's cost.
But what a joy it would be to have just a few pictures with a glimpse of the characters and settings to fire the visual imagination, perhaps point us in the right direction.
An illustration could set the tone of a book even before you'd read it, set some apart from others, even lift the prose into a higher sphere.
As children we see pictures in every book we read, as an adult we're cheated of this small joy.
I don't think I want photographs, too specific, but a black and white line drawing, if colour is too costly, would add a great deal to my enjoyment.