I suspect that it's one of those laws made so the government can say: See? We really are doing something!

Except that's it's not much of anything. I get free coffee refills when I eat out & there really is a limit to how much one can drink. And a surprising number of people don't finish their soft drinks. I see half-full bottles discarded all around town. When we were having work done on the house, the workers often left behind unfinished sugary energy drinks when they left for the night.