Almost free flights out of MEX to the US

Don't know why or for how long, but American Airlines, Mexicana, and Aeromexico all seem to be offering flights out of Mexico City to places like LAX and SFO for $200-250 during the Easter break. Play around with the dates, and you can get a flight from MEX-SFO for less than $200! That means, 5 hours and another country away is now cheaper than flying somewhere within this country.