This May Seem Like a Strange Question...

Someone asked me the other day, and I really couldn't come up with a satisfactory response:

"Why, in English departments, do we write book-length works of "criticism"?"

Oh, in the past, I think it was because there were essentially two options: small things, that is to say, articles which could be compiled in paper journals or book-length publications; or monographs of book length, for book-length publication.

Maybe it's only a question to me because I can't at this point imagine having a book's-worth of analytical things to say on a single topic, or perhaps because, being raised in the digital age, I feel a peculiar affinity for middling-length pieces for which there never used to be any applicable publishing medium. Or perhaps I've read too many book-length works of analysis that really could have been two or three short papers but felt the need to expand themselves to the size of a book for economic (or other?) reasons.

This isn't to imply any sort of value judgement. I'm just throwing this out there.

What do you think? That is, if a) there is a you reading this, and b) you have thoughts.