Buffets and AYCE places like Korean barbecue simply have to enforce the rule against carrying anything out, so as to prevent abuse. Can't stop a flood unless you stop any potential leak with a consistent even handed policy.
It's actually especially evident why, at a Korean Barbecue, otherwise what's to stop people from ordering tons of extra raw meat at the end of the meal and just carrying it out in ice chests.
One man desperate for a bit of fuel is pathetic. Five million people desperate for fuel will destroy a city.