i guess ship fighters is considered a specialist role.
Correct.
Carriers have a lot of specialized equipment that needs to be hardwired into the ship. The ship itself is little more then a hull designed around a frame that is specifically designed to withstand fighters launching and landing. The catapults themselves are also hardwired in and cannot be easily removed without a lot of time and effort.
This also doesn't take into account the other necessary equipment for fighter maintenance and production if they're sticking to 3D printing being the lore. That itself also needs certain care. Once the fighter is printed then it needs maintenance until it's destroyed and printing another one makes sense.
The other modules are designed for ease of removal and installment. Things that don't require a specialized space dedicated to maintaining a whole other aircraft.
It's not like an SRV which just sits there and is ether lowered or raised outside combat at leisure. These fighters need to launch at combat speeds to get in the fight and the deck needs to be able to take the impact of a moving object trying to dock with another moving object. There's a lot of mass and force in there.
The ships listed are designed to have these special needs already in place for fighters. The other ships were not designed for that kind of physical force.
There's your in-game explanation.