Foreigners getting kidnapped is very uncommon. It happens from time to time, although it makes it to the news and they do try to find the kidnappers.
School shootings are extremely rare.
And as a rule, the State Department’s advisories tend to be incredibly conservative. Nobody wants to get hauled in front of Congress because something bad happened to a tourist in an area the State Department said was okay.
People who actually do business in Mexico have access to much more detailed and nuanced security advice.
Same goes for the touristy areas like Cabo and Cancun - the cartels own them all and that's a legitimate source of real, clean income (and dollars) for the cartels, and the last thing they want to do is mess with that. The cartels have a vested interest in keeping the resort towns running as smoothly and crime-free as possible.