The drug cartels aren't making billions because they are stupid.
I don't think they would be willing to kill the goose that lays golden eggs for them.
"...the drug cartels...making billions..."
That brings up an interesting point. What if, as many of us suspect, the drug business is a major funding apparatus for both political parties.
If that is true, then funding and not votes would be the major motivation for keeping the borders open.
Is it not true that by far the greatest number of illegal drugs come across the Mexican border?