Mountains.
This particular experience is in a small town in Oaxaca. Oaxaca is a very mountainous state, with a great cultural richness stemming precisely from its orography: It is so hard to move around Oaxaca that it went practically unconquered during the 300 years of Spanish rule.
Of course, when you look at the network coverage maps, you will immediately recognize our country is a mess full with mountains and areas where... Lets put it nicely, where people are not in the proper economic situation to enjoy the full benefits of cellular telephony. You can look at the GSM voice and SMS, 3G voice and SMS and 3G internet coverage maps for Telcel, Mexico's leading mobile operator. FWIW, Oaxaca is at the South-East of the map, but a similar argument could be pushed in many other regions of the map.
I doubt this little expereiment will cause even a "blip" in the radars of our regulatory bodies (no FCC has no say in how radio frequencies are handled in Mexico, but we have our own COFETEL), because of this same fact: The country is too complex, and nobody is claiming that bandwidth in that area. Of course, were the experience to start replicating along small communities enough to be noticed in a map, a crackdown would surely follow.