FWIW, it's not just picky eaters. I have 3 kids with a rare and life threatening food allergy condition and dozens of triggers. My twins practically survive on nuts as it's one of their few safe foods. No grains, no milk, no egg, no soy, no legumes, various veggies, seeds, and fruits. Their milk and safe flour are almond and they eat lots of pecans and almond butter. So when we travel we take a lot of nut products with us. My oldest is less restricted, but from extreme delays in being able to eat anything he has major textural issues. Peanut butter is one of the few things I know he can and will eat. We try to be conscious of cleaning up their hands after eating anyhow, but in a world where at least 85% of what people are eating they are allergic to, I get frustrated sometimes with the focus on nut allergies and how those who eat nuts need to be extremely cautious and aware of everyone else, but nobody is worried about how the sticky strawberry Popsicle their 2 year old is covered in and spreading everywhere could make my child seriously ill. But yes you are right, when people don't have allergies they don't worry about what they eat, where they spread it, share it, etc. In my dream world everyone would just be careful about foods in general, but that's highly unlikely.
To your point of trace potentially being anywhere, yes that's definitely the case for nuts and just about any other allergen.