It's maybe because some of us 'friggin' geniuses' understand that peanut oil is very *rarely* (if ever) used in American peanut butter. They use soy or other types of veg extract as stabilizer.
It also makes no sense to use peanut oil in peanut butter because the economics are that peanut oil is way more valuable as a pharmaceutical component.
The brand that I dearly miss from back home, which is widely available in the states at nearly any grocery store you walk into, is a natural "whole" peanut butter. The use of the term "whole" conveys to me that its main composition is from the peanut family. They sell "whole" peanut butter here in the UK but here "whole" only seems to mean that they don't add sugar or all the wonderful preservatives, partially hydrogenated oils, and stabilizers and god knows what other chems. For that I am grateful. The downfall is that, instead of peanuts, peanut oil, and salt, they use palm or some other non-peanut oil. To me, that's not "whole" and the taste is nowhere near comparable to what I consider to be real peanut butter. It's not even in the same ballpark.
As for economics of peanut butter in the UK and the pharmaceutical components of peanut oil, I confess to know nothing. But, as mentioned above, the un-peanut butter they sell here is quite cheap and my guess is it wouldn't cost much more to sell an unadulterated version. Peanut oil is a high quality oil. What most of the british pnut butter uses - and skippy and jif - is some of the lowest quality, cheapest oil you can possibly purchase.