Why do we put milk in cereal? Why not other liquids, like water, orange juice, or V8? (Apart from the obvious, that V8 in Lucky Charms would taste like ass.) I tried to Google this but searching for “Why do we put milk in cereal?” came up with a gazillion hits on a gazillion irrelevant things.
Lucky Charms, almost uniquely among cereals, possesses an irreducible assitudinousness: it will taste like that whether you immerse it in milk, water, V8, Pennzoil or Fletcher’s Castoria.
Still, the larger question bears investigation. I suspect that the practice was an invention of the cereal companies themselves, who, having noticed that their products had all the nutritional value and not quite all the flavor of drywall, decided to pitch the idea of a Complete Breakfast, which includes their product, a splash of milk, and maybe half a banana. It would be harder to make this case if people were in the habit of mixing their cereal with Tanqueray or Pabst.
Keep in mind, these are the folks who came up with a product called Grape-Nuts, which contains neither grape nor nuts.