Mexico has rarely had an unemployment problem in recent decades. At least, not as "unemployment" is normally defined, as an excess of workers for available jobs. Rather, there have been few or no jobs available for the willing workers. A subtle difference, but a real one. Mexican (and other) workers have migrated to the US because jobs are available here, not because they have any overwhelming desire to live here permanently. If the latter were true, they would be importing their families (not that some aren't) rather than sending money home for their support.