Its probably very good planning on someone's part. The last buses leave the terminal carrying the guests that were on the ship before you at about 9:00. They'd reach the airport or WDW at 10:00. They need to be unloaded and cleaned, then dispatched back to the resorts. Those buses run pretty constantly from about 6:30 when guest start debarking until 3:00, when they drop off the last passenger from the last plane.
Its just not very convienient for land/sea guests who'd like to get to the ship at 11:30.