I think the peanut butter market is more commercialized and established than the bag-of-peanuts market. The market is probably more stable and enormous.
Another thing is the grades of peanuts. Assuming that they grade peanuts, the ones that get mashed into peanut butter can probably be pretty shitty. But the ones that get packaged in bags probably need to look less disgusting and are therefore probably a higher grade.
Interestingly, peanut butter production facilities are known for being filthy and harboring ratshit.
http://articles.latimes.com/2009/feb/07/nation/na-peanut7http://edition.cnn.com/2014/09/19/us/peanut-butter-salmonella-trial/Another funny thing is that I read a study that took place in Africa, they doing some invasive and inconvenient sampling, and the incentive for participation was a bag of peanuts for the subjects' time. lol