Why do publishers include art inside adventure modules?
I mean, aside from the rare instance where an illustration is required to make the description of a particular area intelligible, or in the case of illustrations intended for the game master to show to the player (which is not what I'm talking about here), I have to wonder why do companies bother?
Adventure modules are, by their nature, utilitarian products. They're meant to be used in actual play. The inclusion of interior art doesn't assist that function in any way (other than noted above).
Do you think that the inclusion of such art helps the game master get a better understanding of the "feel" of a particular module? (In which case, what about the use of generic fantasy art, such as we see today in the licensed clipart used in some modules?) How about pictures of particular characters/NPCs/deities/etc.? Why include them if they aren't intended to be shared with the players? Doesn't that defeat the purpose? Do modern publishers use such illustrations as a sort of atavistic homage to the way modules were done in years gone by? In which case, why did TSR include such art in the first place? From my recollection (I've not actually looked through the modules in my collection; so it may be wrong) the old Judge's Guild modules had much less art than their TSR counterparts. Why did TSR add an extra couple of pages worth of art? Just to round out the page count to a number divisible by 4?
I'd be particularly interested in hearing from those out there who've published their own modules, but all are, of course, welcome to comment.