I've been knocking my brains out searching for good sightings in Mexico, but so far have found nada. Well, not much, anyway. Why should this be? The American cordillera is a series of mountain ranges that stretches essentially from Alaska into Mexico and encompasses much of bigfoot's presumed range. It is seemingly much more likely that these animals would have found their way into Mexico's Sierra Madres mountains, which is prototypical bigfoot habitat, than that they would have wandered across the much less hospitable American plain into the eastern ranges and Florida. What gives?
Language differences may account for few Mexican sightings in US databases. More troubling are cultural differences. Each culture has it's legends, myths, and--more to the point--boogeymen. Predominant in Mexican cryptozoology is, of course, chupacabras. Do they have their monster, we have ours, and never the twain shall meet? I think this could be significant in the mythological/sociological sense, and may speak to a phenomenon that skeptics often trumpet--a sort of 'mass hallucination'. Somewhat akin to racial memories, I suppose, these sorts of indigenous legends would have some difficulty disseminating across geographically proximate yet culturally separated populations.
The border guard sure as hell ain't keeping 'em out.