Why no guns on carriers?

The (never-built) German navy's Graf Spee's original plan included multiple 16-inch cannons, and the Soviets later used them on both the Kuznetsov- and Kiev-class carriers. Why can't we add them to carriers in HoI4? It's definitely not because they're useless, 'cause if that was the reason, there are plenty of other things that're in the game that wouldn't be.

If I can build a midget sub, I want to be able to build a ... cruiser carrier?