Why is the local law and order in Mexico so poor?

Because Mexican gangs are so rampant, the weapons and equipment of Mexican gangs are no worse than those of the police, and the number of gangs is no less than that of the police.

The reason why Mexico is so chaotic is that there are many gangs in Mexico, and they often fight with each other for territory and drug sources. Many policemen, driven by interests, also joined gangs. Therefore, when Mexico cracked down on drug traffickers, it sometimes used regular troops.

Mexico is so chaotic, which is also the main reason why the United States insists on building a border wall.