LogFAQs > #964684963

Because it's more expensive to make and putting a full loaf on the shelf would tank sales because people would tend to avoid the loaf that obviously cost twice as much as everything else available. By introducing the extra cognitive step of having to compare the per-unit price, you get fewer people recognizing how much more expensive it is (and in some cases, even saying "ooh, rye's normally so expensive, but I'm getting it for the same price as other bread" and therefore buying it preferentially).

Of course, it's not actually *that* much more expensive to make because flour costs are generally a pretty small component of the overall price of bread (unless you're dealing with unusual specialty flours, of which rye is not one) and you can't replace all of the flour with rye flour anyway (rye flour's gluten is too weak to support bread, so you need some wheat in there), so it's not that difficult to sell it for the same price, especially if you bump the others up slightly to keep the same average margins. But that's more the realm of specialty bakeries than what you'll find in the grocery store.