So he respects rules that some random Mexicans made up over the lives of his crew?
You can't sell drugs in someone else's territory/neighborhood without expecting backlash. Those aren't Mexican rules, those are drug dealing rules.
If you've got the power/muscle to take over, then
But Franklin didn't, his crew was small as hell, most of them didn't even know how to use guns. You sell in someone else's territory without the muscle to withstand what comes next, then shyt might go bad, which is what happened.
Which is why Franklin and Jerome told everyone not to sell on Pico. Mexicans sent them a warning, Kevin was about to respond recklessly, putting everyone's lives in danger.