Because none of those have any real basis in reality. Case in point with your concern over Fallout:
You seem to have a very outdated perception of what Fallout is, too, for the record; within two weeks everywhere but the direct impact zones are safe and Fallout is no longer a running concern. Hell, there are hundreds of people who have been living in the Chernobyl Exclusion Zone since the events there happened in 1986 and that's many times worse-in terms of radioactive output-then what a nuclear bomb would do since we are talking about a reactor with much more fuel.
Possibly my ideas on fall-out levels are 'outdated' but fortunately we never found out. However even if that doesn't cause direct impact on Mexico - in which case other northern hemisphere nations which avoid direct attack also come into play - my other points are valid.