My view is the per jump pricing of CT is a compromise among several competing agendas, and setting agnostic for the most part except for the pro-trade agenda.We all know there's some form of price cartel in interstellar passenger and freight rates.
One speculation could be that's it's the government subsidizing it, but instead of using the rates to ensure trade and communication affordability, it's forcing the customers to actually directly subsidize it.
Giving an absolute floor to pricing keeps the local J1/J2 distribution of goods and resources in business and not subject to destructive price wars between each other or sector plus lines. It gives a guarantee to servicing debt that makes bank loans for ships viable.
Giving the same as ceiling helps shippers’ commodities to travel farther, giving them bigger markets and an edge to megacorps production at IND planets.
Another factor is financing ships- large lines are either rich enough to commission their ships outright without financing, or gain lower/no interest loans from the megacorps wishing to expand their tonnage/routes. Without that cost albatross, J3+ becomes far more viable.
Finally, compensation for services at a level far beyond that able to be accessed by even a local line. Megacorps and megalines are probably joined at the hip and the lines can make bank in other ways to subsidize high-J routes. The aforementioned financing for capacity, a cut of 1000s of tons of speculative cargo for minor markets, and possibly a cut of sales from products moved or money moved through shells- plenty of margin for a system geared to the multi sector interests.