For illustration purposes only, lets say there's unit 1, 2, 3, and 4. Each unit allows 50 tags for zebras(200 tags total). On your application, you get 3 choices for a unit. 200 names will be drawn total, but say nobody has unit 4 listed as a choice, we have 50 leftovers for sale in unit 4. It's not the Dept's fault, it's just how the system works.
"A man may not care for golf and still be human, but the man who does not like to see, hunt, photograph or otherwise outwit birds or animals is hardly normal. He is supercivilized, and I for one do not know how to deal with him." Aldo Leopold