We are not talking about small time thugs or minor criminal gangs with little influence outside a small area. The Mexican cartels have a world-wide footprint in every business and industry that exists. They have little difficulty obtaining anything and everything they wish to have, and very few obstacles in moving (literally) tons of US dollars in cash anywhere to achieve any goal, all fueled by an insatiable demand for drugs in the United States.
Additionally, the cartels operate with relative impunity within Mexico. Politicians, journalists, bankers, police, and military commanders are owned by the cartels. It is not an exaggeration to say that the cartel bosses are on a par with, if not superior to, any government agency that exists in Mexico.
An unfortunate truth is that most of Latin America has a history of absolute corruption at every level. In everyday commerce nothing can happen without payoffs to every level of bureaucracy. Any measure applied to the various groups of powerful or influential interests in Mexico is limited only to the level of corruption, not any absence of corruption. There is no history or human memory of any other way to live or to do business.
Beautiful country, rich culture, warm and wonderful people, all ruled by despotic thugs and aristocratic arrogance.
Small arms ammunition? No problem, send a couple of lawyers to buy the company. The lawyers will not fail because they know that their families' survival depends on their success.
Problems with customs officials at a port of entry? No problem, send someone to show those officials photographs of their wives and children, their homes, their schools, their pets, their friends at a nice party.
Several of the major Mexican cartels have wealth and influence that exceeds many national governments, and literally armies of mercenary gangs to enforce their will in every way.