Why are we measuring our food by weight, and not by volume?

We measure our food by weighing it in ounces on a digital scale to get an accurate barometer of what we’re eating. Using volume is inaccurate. For example, 1 cup of carrots does not weigh the same as 1 cup of lettuce. Plus, one could stuff a cup really, really full with food, whereas an ounce is an ounce—the scale doesn’t lie.