Perhaps there's something in the additives that go into the commercial ice cream that increase its freezing point? Similar to the difference between putting a glass of salt water and a glass of fresh water into the freezer. Perhaps the lack of such an additive in the home made ice cream naturally have a higher freezing point than the commercial stuff, therefore making it hard as a brick by comparison to commercial ice cream in the same freezer?
Remark: I've spent waaaaay too much time in a chemistry lab.


