Note that one of the major cartels was literally founded by Mexican special forces troops.
Well, to be slightly more accurate, Los Zetas was originally founded as a new security/enforcement arm for the Gulf Cartel, but ultimately broke away and became its own cartel. But it still was literally founded by a retired Special Forces officer who recruited over thirty Special Forces troops to desert and join him, and that's specifically what made them so dangerous and successful.
*Looks at arming & training of special forces that became the Zeta cartel*
To be fair, they were legit special forces troops at that time, and no one had any idea which specific ones were going to join the cartels for many times the pay, any more than the U.S. Army itself can predict which of their soldiers are going to join PMCs for many times the salary they can make by continuing to serve.