Mexico’s first openly non-binary magistrate and prominent LGBTQ activist Jesús Ociel Baena Saucedo was found dead at home in the central state of Aguascalientes on Monday.
Legalization would bring in more government meddling, not less. Exactly as you said, the government doesn't have that much power. Cartels currently have full control of production, distribution and profits. They do not want regulations, taxes and dealing with competition in uhh... less confrontational ways. That's even if they'd be allowed into the market, which is unlikely.
If you want to toss out that argument, fine. Cartels don't want legitimate competition at all. Legalization would flood the market with startups that they couldn't control or compete with.