I presume you are speaking to the Reno Aircraft bundles? They have to be separated as different aircraft because each one of them is a unique aircraft model. They do not share the same cockpits or in some cases, external features as well. Also, the T-6 is split in the aircraft selection menu because some of them are ATs and others are SN-Js and then the T-6 too. The aircraft menu sorts alphabetically. Just the way the game runs.