I suppose I can't say that I know with absolutely certainty that they were safer, but we would talk with locals and got a general feel for what places are more or less safe.
One explanation was that the cartel members have families too and keep the cities their families live in free or more free of that sort of trouble.
I would look into place like San Miguel De Allende, Valladolid, Puerto Escondito, Puerta Vallarta and the small villages north of it, Todos Santos, Oaxaca, San Cristobal De Las Casa. Guanajuato.