Why do drug cartels continue to exist in Mexico then? The Mexican army easily outguns any one of them.

So clearly it's possible to be very violent and continue to exist, so if your goal can be achieved by violence and you're not directly attacking powerful interests within the Mexican government, you'll be fine. If some entity wanted to stop illegal immigration and started paying cartels to ambush immigrants and send the message the border is closed, who is going to stop that? Think George Soros is going to fund paramilitaries to attack the Jalisco cartel? Do you think George or his kids would live very long if he did?