Probably because the aim of drug cartels is economic rather than ideological or political. But if acts of the cartels are terrorism, then you'll have to buy extra insurance that typical insurance doesn't cover. This could be costly to everyone since drug dealing in the US commonplace. Say you get in a car accident and the dude is a low level drug dealer. Since drug dealing is aiding a terrorist activity (selling drugs), your insurance provider won't have to cover it unless you had a terrorism rider on your policy.