UAS and AEF tend to work Weds-Sun primarily so you'd be wasting an airfield of 2/5 of the normal working week if you separated them up.
Also a single airfield could simply not cope with the level of flying 3FTS require if you put all 4 EFT Sqns plus the CFS task into one airfield. It also spreads the risk of the EFT task delivery failing in case one airfield should go Black for any significant time.
I believe the segregation you refer to is within the supervisory chain rather than geographical locations.