Back when specialty compartments were more of a thing, the liners were the only ones that could take certain classes of compartments.
There was a lot of outcry about that, and it eventually went away as a concept (except for military). I rather doubt Frontier will want to go back down that route, although a dedicated amount of passenger haulage might be a thought, in the same way people are asking for a dedicated amount of general haulage.
I tried to add first class cabin to my 'Conda and it stated passenger ships only, so it looks like it hasn't completely gone away and that was only a week or so ago.
Your "problem" is a general symptom of the fact that Frontier uses the ship model to generate the rules of construction instead of having a procedural ship building methodology. It will never get properly fixed as long as the "Compartment" system exists because, instead of installing volume based accommodations, you get this borked up class system.My problem isn't with luxury cabins, the beluga liner can only fit 150 economic class cabins which is ridiculous.