Yeah it may not be gate revenue but as WFU03 said above there's definitely money sharing happening to make it more worthwhile to play in packed US stadiums rather than playing in less profitable Mexican stadiums.
Yeah, when I brought up games in Mexico to my friend, he laughed and made it sound like that was not going to happen anytime soon because it made no financial sense to have them there.
In 20 years, if the games are must watch tv in both countries, maybe?