Blowing up brown people in a desert on the other side of the planet means it’s a lot harder for combatants to reach the United States.
Blowing up people who have made a career out of subverting border security, and who are only a few hours travel from the border, involves a lot of risk to the mainland.
Congress would never risk exposing the charade of their trillion dollar security blanket by green lighting an operation like that.
It also gets tricky when you consider how deeply the cartels must be involved with parts of Mexican government. The line between policing action and outright coup could get blurry really fast, which just leads to more issues.
Probably best if we don’t stick our noses into another decades long conflict with no quick resolution in sight.