I didn’t know the cartels were big defenders of the 2nd Amendment.
The Cartels distribute guns to their drug marketeers (pushers) so they can protect their market from competitors. When they control their market, they know their addicts and will maximize their drug purchases from them. A competitor does not know the addicts and their sales will experience a drop, which the Cartels don't want.
The Cartels get some of their guns from Mexican police departments who sell them to supplement their operating costs. The Cartels know how to smuggle those guns across the border. Murders by drug gangs using those guns are the major cause of murders in our cities.