Why do some products shrinkflate, while others don't?

The things that shrinkflate can, basically, while increasing profit. If you look at the differential in price between 1 pint, 2 pints, 4 pints and 6 pints, you can see that it's absolutely pointless to shrinkflate. It is SO much cheaper to buy a bigger container that you don't really need to bother- you can just play with the price for each size. Bread, as others have said, varies SO much in price all you have to do is vary the offer. Milk and bread etc are both also v cheap at a basic level. There's not much profit in it anyway. But note that BUTTER has shrinkflated- lots of butter is 200g now and not 250g. Chocolate etc is expensive for what you get,so you can shrinkflate and people will still buy some.