Know why?
Because the threat IS there. Spoken or unspoken.
If the leaders of LA would have stated that anybody looting after a mandatory evactuation will be shot, there would be almost zero looting,and fewer people would have been killed by lawlessness. It would also made rescue easier, as less resources would have to been diverted. And people who actually needed food supplies would have had a better chance of getting them through orderly distribution.
Instead, you have chaos.
Your choice.
Play nice with the looters and get chaos, death, destruction.
Get tough and save lives.
Cause and effect.
Actually, there is quite a bit of looting in FL, and they arrest them, so they pretty much know they won't get shot.