From the linked article (which may or may not be accurate):
It also became apparent that scores of other aircraft continued to operate in and around Mexico over the timeframe. For example, Iberia's Thursday service from Madrid to Mexico City landed without incident.
As wiggy says, I'm sure the decision was made carefully after considering the pros and cons of all the options. But I'm curious as to why landing at another airport in Mexico would not have been preferable. Crew issues? Lack of horse-handling facilities?