Because no one drinks a pint of pork bellies. Chesterton's fence applies here: "In the matter of reforming things, as distinct from deforming them, there is one plain and simple principle; a principle which will probably be called a paradox. There exists in such a case a certain institution or law; let us say, for the sake of simplicity, a fence or gate erected across a road. The more modern type of reformer goes gaily up to it and says, 'I don't see the use of this; let us clear it away.' To which the more intelligent type of reformer will do well to answer: 'If you don't see the use of it, I certainly won't let you clear it away. Go away and think. Then, when you can come back and tell me that you do see the use of it, I may allow you to destroy it.'" (Even the fiercest advocates of the metric system never seem to realize they're still living their lives in imperial amounts, just with metric labels. No one ever had the thought, "Hey, 355 is a good amount of milliliters for the average person!") Imperial units are based on human needs, human experience, and the human body. The metric system isn't an attempt to improve the economy, or increase scientific understanding; it's based on a belief that universal rules and standards imposed from on high can make people better. And like Mal said, I do not hold to that.