I think that for some, they see this less as an opportunity to bug you at midnight, and more an opportunity to call when they remember to, and just leave a message for you to at least get the ball rolling.
Others seem to do it because they don't have the sense not to. I soon discover this lack of sense seems to pervade many other areas as well. Like wanting a price for a lawn seeding without ever seeing the yard. (sounds like I'm thinking of a specific case, doesn't it?)
I do get some that look up my home # and call that. I explain at the first call that if they want to talk shop, call the shop line. I don't talk biz on the home line. And if they say "I can only reach you (at 9pm) at that number", I say "There's a reason for that." I very rarely go on to explain that during the season I put in between 80-100 hours per week, so during those few hours that I'm not answering calls, I'm not answering calls. Period.