This is a great question and we wish we had a better answer. All we can say is ..."because of the blue whales."
Do you know about the blue whales? They're the largest animal in the world, yet their throat is only about the size of a grapefruit... do you know why? Because that's the way it is. :)
You can, however, rename creative files that you do not intend to use or that were inadvertently uploaded to keep those files out of your way as you create your campaigns.