I suspect that Telmex ISP, Mexico biggest by far, found a very surgical way to prevent relays.
Atlas only show a small group of Mexican relays, all of them in other ISP.
Tor client (and I2P) works well, and the hidden services too. Pluggable transports and/or the tor alpha make easy to bypass this little nuance.Â
Usually Telmex ISP does not implement any kind of wide censorship, is generally pretty open. I think this a very smart attack to tor infrastructure, it does not prevent tor in general, but almost all the exit traffic will go to outside the country, and little traffic will mix between Mexican tor clients that choose having a relay.
For me, I will try to make stone arguments for a little David/Goliath action, because Telmex works like "that is not a problem if others are not complaining" , "Facebook is working, right?"