If you really want to know, I can't recommend the book "Seeing like a state" enough.
TL;DR: For government officials who are charged with supervising regulations over tens of thousands of areas, it's already more than complicated enough if each of those areas has a single use designation. If you allow all of those to have multiple designations, it becomes too complex for humans to administer and so they don't allow multiple designations.
TL;DR: For government officials who are charged with supervising regulations over tens of thousands of areas, it's already more than complicated enough if each of those areas has a single use designation. If you allow all of those to have multiple designations, it becomes too complex for humans to administer and so they don't allow multiple designations.