The only reason I could see for it is if somebody somewhere hasn't done the exam yet - but they tend to restrict the same subjects each year so that can't be the reason. Or if it had a lenghty extract from somewhere (like a book) and they didn't want to give people free access to that, but this didn't apply to DD202 last year.
They must have some reason for doing it, and it can't really be financial because they sell papers for £2 or so and thus can't make much.
But then you don't need the exam paper afterwards - if you look too much you'll end up torturing yourself because you forgot to add something, or maybe should have done a different question. Just put it out of your head and move on.