Like most people in the U.S., I love peanut butter. The kind I buy contains just peanuts and some salt. But when buying whole nuts, the cans of peanuts are the cheapest, and in mixed nuts the cans containing peanuts cost less than the ones without peanuts, implying that peanuts are less desirable/cheaper that other nuts. And yet, peanut butter continues to sell. Why is that?
Because it’s the cheapest?
Because it’s delicious!
Well, for one thing, peanuts aren’t nuts, they’re legumes…
Peanut butter sells because people like peanut butter. There are other nut butters, but in my experience they’re 2-3 times more expensive than peanut butter, and not nearly as easy to find.
If I could still eat peanuts (damn allergies!) I’d probably by them by themselves just to enjoy peanuts, as well as buying other nuts to enjoy them. Certainly, it would be a cheaper snack than tree nuts. Peanut is a good flavor, after all, nothing wrong with, and nothing wrong with them being cheaper.
You are comparing apples to oranges. As a singular comparable attribute, more expensive does not equate to better.
People like peanuts. Peanuts are cheap. Both of these statements are true, and there is no conflict between them.
It’s also true that some people like other nuts better than peanuts, and sometimes these people are willing to pay more for them. That’s why there’s cans of mixed nuts on the shelves without peanuts, and why they’re more expensive.
Only 1.1% of Americans are actually allergic to peanuts. Are you sure you’re one of them?
peanut butter is a palatable nut butter.
Yes.
I have a medical file dating back 36 years documenting my allergies, including two ER trips involving anaphylaxis. Peanuts were a late arrival to the list but I am most definitely allergic to them. Fortunately, not my worst allergy but I do try to avoid them as much as possible.
Cool, you’re part of the 1%! 
Uh, yeah… lucky me, should probably purchase a lottery ticket… 
I imagine the fact that peanuts are domestically grown and relatively cheap and easy to grow (assuming certain climate & soil) has some influence on their cheaper cost relative to exotics such as Brazil nuts.
that might be a PayDay.
You ever hear of a walnut butter and jelly sandwich? Uh-uh! Peanut butter, the all American food!
Peanut butter and jelly sandwiches
Peanut butter and bacon sandwiches
Peanut butter on celery sticks
Peanut butter on English muffins
Peanut butter on apple slices
Peanut butter on crackers
Peanut butter and banana sandwiches (Elvis loved 'em)
Peanut butter cookies
Peanut butter and chocolate
There’s just no limit to the wonderful things you can do with Peanut butter. And I oughta know. 
Because it’s relatively inexpensive and tastes great as a butter? I’ve tried other nut butters and, while they’re good to great, I like the low cost and availability of peanut butter. I’m not entirely sure I understand the question here.
Ok, I’m not questioning that people like peanut butter; I love it as much as anyone. But what I’m wondering is why people don’t like peanuts as much as peanut butter, why they’d pay more for a can of nuts because there aren’t any peanuts in it.
Context is important. If you have a box of Crackerjack, you’re disappointed if there aren’t enough peanuts. If it’s mixed nuts, you’re disappointed if there are too many.
Anyway, people do like peanuts, as evidenced by the fact that cans, bags, and jars of peanuts sell quite well.
because once upon a time, companies selling cans of “mixed nuts” were loading them up with peanuts to save money. Then people started bitching that if they wanted a can full of peanuts, they’d buy a can of goddamned peanuts!
Peanuts are relatively cheap not just because they’re less desirable than other nuts, but because they’re cheaper to grow. Most nuts grow on trees, which take years to bear crops. Peanuts are an annual crop, so you don’t have to invest as much time or money to grow them.
Some nuts would probably make awful butters. I suspect walnut butter and pecan butter would be terrible. Macadamia nut butter would be too rich, and I expect Brazil nut butter would be, too. Pistachio nut butter might be good, but would be so different from peanut butter that I don’t think you’d want to use it for the same purposes (anyone for a pistachio butter and jelly sandwich?). Has anyone been crazy enough to make pine nut butter?
Some of the difference between different types of nuts is in their textures, and this difference is eliminated when you make nut butters.
There are other nut butters. The most common are almond butter, cashew butter and sunflower seed butter (yeah, I know sunflower seeds aren’t nuts, but technically neither are peanuts). I have had sunflower seed butter and found it to be overpowering. Both almond butter and cashew butter are very expensive, and I don’t know that they’re different enough to justify the expense if you’re just going to make a sandwich with nut butter and jam.
Peanut is easily in all groceries even in a gas station that have grocery store aside from being cheap.