Since they got rid of the old Federales (who acted as an organized crime outfit who also had badges) and thus created a massive power vacuum that was then occupied by the gangs, who evolved into the cartels.
The Federales were originally the losers of the Mexican Civil War, mixed in with some bandits, anyone the central government at the time could not control, they were pacified and wrapped into the government by making those forces into federal police and giving them semi-autonomy in their own regions. They basically immediately went full mafia, but it was a form that severely limited any other group, and they didn't need to use fear to maintain order because they also had the authority to arrest people. Then in the late 80's and early 90's there were some big scandals that showed that a crime wave in the US was being perpetrated by the Federales. The US leaned on the Mexican government to deal with it, and their solution was to decree that anyone who had ever been in the Federales could never work in law enforcement again.