Your concerns are noble. The cost of tolls will fall right after gobernacion chops the price of comistibles to an affordable level.
Toll roads get refinanced over and over and over and over and over and over and over (is that enough overs?) again. They win tax credit and repamyent concessions from gobernacion and SHCP.
Of course there would be more customers with more traffic. But this is Mexico. They get it into their head that whatever the have is worth so much money and they will freakin' DIE before they would lower the price. No es la costumbre.
Anyone who comes to Mexico with an "ought-To-Be" rather than a "Is" sense of perspective is going to leave disillusioned, disappointed, angry, frustrated and confused. Probably the # 1 reason for expatriates to bail-out after a few years. Mexicanos have a joke "Ay caray! Here come some gringos with a million questions". This says volumes about the difference in cultures.