Well, tell that to Europeans, who don't use millilitres to measure their flour or sugar by volume - they use bizarre units of volume called "grams of flour" or "grams of sugar". Check their cup measures! It's crazy.

Apparently it works perfectly fine for household cooking to use units of volume for flour and sugar. Close enough is good enough!

If you need a particular amount of flour, you can't express it in volume, since 250ml of flour may be too much or too little depending on how tightly the flour is packed. For reliable baking, measuring flour by volume is too inaccurate, you need to weigh it so you know how much flour actually went into that cup.