Because the drug cartels are large, violent, and more than willing to cross the border with military style weapons to attack Americans. So trickling their criminals back to them is an awful lot more cost effective than stationing two or more US Army divisions on the border.
“o trickling their criminals back to them is an awful lot more cost effective than stationing two or more US Army divisions on the border”
Sending their criminals back to them in little, tiny pieces would be even better :-)