Because EVERY SINGLE SQUARE INCH OF EVERY SURFACE MUST MAKE PROFIT.
I would complain and stop shopping there, and encourage others to complain as well. Hell leave the doors propped open to help people see what's inside, even though it'll run up their electricity bill and spoil the contents. Aslo remember to bring in one of those window-cracker car safety things and have a go at breaking the screens if you want to be even more rebellious.