Celebrity Circle is used mostly for private event drop offs, but besides that not much. The area for private event pickup/droppoff really can't be changed though and it would never be able to work with other buses coming in and out - not only due to room there, but because the point of a private event is that it's, erm, private.
Also, if they were to move buses there, Universal then has to up the security at Celebrity circle, which is currently one metal detector. They also lose out on any potential business from people coming in the current way. No one is stopping at Voodoo or a restaurant for example if the buses are there.