Some farms are conventional, some are organic, some let’s their cows move more freely than others, some use more antibiotics others less, etc

So no, milk is not just milk. Animal welfare as well as animal intake are big parts for why certain brands can take a steeper price than others

The only places I’ve ever witnessed unbranded milk, are in very rural locations at which you pick it up at the literal farm that produced the milk and that’s a brand in itself