What a misinformed OP.
They ain't scared of America, they don't want to lose ties with drugs. This is a fact. Also, most Cartels have rules where innocents aren't to be killed. Only time innocents are killed are when they are family members of rivals.
The perpetrators in this case were lucky they were just given to authorities, instead of being skinned alive and having their eyes gouged out, and then having their heart and intestines cut out and eaten.
Also This is a small, and fairly new cartel. You don't see the Sinaloa Cartel or CJNG Cartel ever doing this. CJNG cartel are made up of former military members, they are ruthless and sadistic as fukk. They recently got into it with the Mexican military and the military fell back.