It would be fixed overnight if the US didn't import. That is at least as much a part of the problem - the bad neighbour.
Mexican drug dealers who snuck into America import drugs from Mexicans in Mexico. Americans to blame. Nice victim-blaming.
I remember the US briefly had a president who wanted to protect the US-Mexico border but he got called racist by the people who profit from importing problems into America.
The OP seems to be making the commonly made point that drugs wouldn’t flow into the USA if there were not lots of Americans (rich and poor) who wanted to consume said drugs. Before you attack me, I am not trying to argue for or against that point, just noting that it is a common one on any of these HN threads.
That doesn't change the facts. The problem is the buyer, not the seller. If Mexico doesn't sell, someone else will. If Americans doesn't buy there's no other buyer. Mexico isn't the problem. The rich neighbour with bad laws is.