Because it's dry. It's so dry that it dries out the mouth eating it. Plus it's hyper processed vitamins and grains and minerals... Those digest easier with milk.
TONY THE TIGER ON FROSTED FLAKES; They'rre Grrreat! They'rre Grrross! TONY THE TIGER ON FROSTED FLAKES THAT HAVE BEEN IN THE MILK FOR 1 SECOND TOO LONG.