It’s because of the importance of publishing to the career advancement and tenure process. I was having this conversation with a political scientist a while back, and he was shocked about how close historians guard their working in progress. To give an example, when I signed the contract for my most recent journal article, it had all sorts of conditions about not sharing the pre-publication version until it was published. In this case, it was an article about the Spanish flu in Egypt, which became a topic of great interest last year, and I tried to ask if they might consider doing a pre-pub version and they said no. (I was very annoyed).

There are a couple of newly emergent kinds of things, like academia-dot-edu where people sometimes put drafts and open them up to comment (another is ResearchGate), but, on the whole, because of the way the humanities puts such a premium on NO SPOILERS before publication, there just isn’t much.