Some of the companys are probablly just making money others are operating in the negative and are now just for a tax purpose, maybe some of those toll roads have all ready gone broke and where taken over by Secretaria de Comunicaciones y Transportes (SCT) and the only thing that they have to do is maintain a road that was not financed by them, the Spanish banks invested a lot of money and have since gone broke in Mexico and in Spain, and the projects that they invested in are at a practical stand still.
In the US it makes sence to think as you sugest, in Mexico prices rarlly go down specially when the government is involved in any part of the operations,
there is just to much corruption.
As I stated before some of the oldest carretaeras de cuota are still in operation and they seem to be doing OK, the cuota to Cuernavaca has a branch to Cuautla, that was not part of the original, and there is another one from Puebla to just east of Cuaultla it probably will be part of the circle that eventually will bypas Mexico City.
Some of the things that are done in Mexico and Latin America can be baffling to the gringos since they just do make any sence at all, best is to enjoy your cerveza under the palapa and latter take a siesta.
You can not compare the way that the toll roads operate in the US and how they are operated in Mexico there are some facts that we will never get to know at all, we can speculate as much as we can and want, we will not have a correct answer nor the facts.
Manana sera otro dia.
navegator