My store has a few different brands of coconut milk. Some of the unit prices are per pound, while others are per quart. I make the approximation that coconut milk has the same density as water, which is two pounds per quart. The unit prices are all odd three digits numbers. It's a pain.
You could have one person who works in an office somewhere who's responsible for itemizing inventory for the whole grocery chain. They could solve this problem (maybe automatically!) with a spreadsheet. They could also solve the problem of tomatillos not being registered in the self-checkout catalog. But what is that person's salary paying for in the company's eyes?
To be fair, maybe the real explanation is "lots of stuff, shit happens." And it's only a factor of two (for watery goods, anyway).
