Chaosium prioritizes their projects and puts them in a queue.
Despite the fact that those pregens would take, relatively speaking, no time at all to finish, instead of using a day or two to finish them, Chaosium doggedly sticks to where they are in said queue. So if the queue right now is: Solar, Sartar, Darkness, GM book, Chaos, Pregens (for example), they won't touch those pregens until those five other projects are complete. Even if Chaos, say, will take 50 days to layout and the pregens will take 1, they'll still do those 50 before that 1.
I think it's ridiculous, but I think a lot of things they do are ridiculous.