Containers of ice cream are sold by volume, not by weight. Some ice cream manufacturers pump air into the ice cream before packaging it. Why does this practice make the ice cream more expensive to the consumer?

Ok so say a pint of ice cream is 7 dollars. And we have two different brands. Same price, same flavor, same package. One pint is filled to the top and is very dense. The other is filled an inch away from the top and is light and easy to scoop through. In processing they both were filled to the top but the lighter ice cream had air pumped into it. This air settles at the top as the air is less dense than the ice cream and still gets trapped in the ice cream as well. This costs the company nearly nothing to do and nearly doubled the mass of the ice cream in production. Leading to them saving a lot of money while charging the same price. Technically this brand is more expensive because you are getting less than what you are paying for.