Unfortunately, they are. Still, a lot better in terms of detail and quality than most of the ship kits it has to be said.
I think the reason they did it this way is a few fold:
"Shipkits" on regular ships are not actually "physically there". You can literally pass through those tiny winglets, spoilers, nubs etc. with another ship or any other solid object. They are truly decorational. They could not even think of applying this approach to Carriers, youd be able to clip though entire sections of the carrier, engulfing even Cutters.
Secondly, I think this opens up the opportunity for future "classes" of carriers to be sold, if only as a cosmetic. We have never seen additional parts to preexisting ship kits offered. (Just new styles, such as raiders)
Thirdly, I think this was a design decision based on leftover art assets from the scraped "support vessel" idea frontier floated out at the very early reveals of carriers last year. Not wanting these assets to go to complete waste, they altered them up a bit and turned them into what we now know as "Class kits"