If you try it at home you'll realise combining milk, butter and sugar in a bowl doesn't create ice cream. And when you figure out how to create ice cream you'll realise moving said ice cream to a place where you can sell it requires extra steps too

You also have to learn how to do it without adding things like listeria which seems like a difficult task for at least one brand after multiple rounds of recalls.

How does the cost of chilling, packaging, and moving 1/2 Gallon of ice cream differ from 1/2 Gallon of frozen dairy dessert?