Category "volaris"

Why would a "flexibility" option for a flight ticket be only available to the residents of the country where the flight is happens?

I was looking at some Volaris tickets for a flight within Mexico, and read that their "flexibility" option is only available to residents of Mexico. What could

When flying with Volaris, what difference does it make between flying to TIJ or TJX?

In searching flights with Volaris, the destinations offered include "Tijuana TIJ" and "Tijuana Cross-Border Xpress TJX". What is the difference between these?