I don't know the exact year that containers for ice cream bought in the freezer section of supermakets started decreasing, but it was in the last few years.
My recent purchase of Breyer's Lactose-Free Vanilla Ice Cream found myself looking at what seemed like a box that had shrunk even smaller than the last time. Maybe it seemed smaller because I have been buying other brands in the last year, such as Edy's, which has kept a heartier ice cream quality than some other brands that have added air to their ice cream (boosting the volume size, thus decreasing their cost per unit per weight) and packages their ice cream in what seems like a larger container (maybe it's an optical illusion in that their container is more of a cylinder type vs square shape).
The Edy's package was 1.5 quarts (1.42 L). The smaller size allows for easier storage in a small top freezer, though.
I bought this due to the "buy one get one free" offer at a local supermarket. The price of one container was $6.30. From the offer, that meant that one container was $3.15. It wasn't so long ago that one container of ice cream sold at a non-sale price of $3.00 and that was when the container was at least 25% larger. At to that the more air that some companies have been putting in to the making of their ice cream and you will get a better grasp of how much more expensive ice cream has become by weight.