Probably liability and insurance.

What do you think would happen if you offered huge drinks, unlimited amounts or large capacity drinks of caffeinated, or energy supplements in a machine. What do you think a bored teenager with a bunch of his friends on a Friday night would do? They’d try to drink five gallons of Monster Energy just to see what would happen.

Someone would suffer a heart attack or some medical emergency and lawyers would have a field day milking concerned parents and restaurants with access to millions in insurance.