I had thought of this as well-- technical limitations demanding that the number of existing carriers remain low. This would mean that the pricing would be set so that only the most dedicated grinders would be able to have them. If this is the case, then it's an odd choice from a development standpoint. It's a lot of effort to go through for less than a tenth of a percent of the players. Or perhaps less than a percent of a percent. I understand that part of the justification is that they're still for "everyone" because visitors can still dock and use services, and players can collaborate (to a point). But currently there isn't much to encourage visitors to make use of services either, unless you can strategically locate the carrier to make it more convenient than hitting a station.
Instead it feels like it should be an end-game feature; a goal that is within reach for experienced players who have done most/all of what the game already offers, and are sitting on a pile of cash. I feel like I'm in this category, as I've played for years, over thousands of hours, triple elite, 3.5 million lightyears traveled, and sitting on billions. And yet, in the current state, I'm not sure I can handle a carrier. Simply because multiple hours per week (on average) of mining to cover the upkeep isn't appealing. Nor is about 5 hours of mining per jump to fuel it (it would be better to mine LTDs and then use that to pay for fuel, but that's not an option if you take the carrier away from the bubble). 5-7 billion per year, plus fuel? No thanks. I don't want to pay for the privilege of having to do more grinding or else I lose my shiny toy.
So if that's meant to intentionally discourage end-game players, it's working.