How many monitors do you have?
I personally use a combination, 2, 3 and 7. I really would like to not have to have task bars on all my monitors just to get it on one, also most of the functionality of the taskbar on the main monitor doesn't work on the secondaries, making it kinda useless to put it on all monitors. Anyone, especially gamers with multiple monitors really don't want to be forced into having it on the primary monitor since it will always be covered regardless.