If they started charging a cancellation fee I'm sure it would either be equal to or greater than the preorder cost.
I'm surprised people could cancel preorders and get full refunds. I assumed they were like non-refundable deposits. Usually if you put a deposit on something and back out, you lose your deposit. I've personally never preordered as I want to wait for reviews before I consider buying a game. With so many people preordering companies are basically getting free loans, I don't get why consumers are so ok with this when they're getting so little in return.