Well, when it comes to nerds specifically (real ones, not fake ones like Blob the Stupid of House Fat) it's envy. Sure, nerds may be smarter than the normies, but what do normies do? Have parties, date, stay in shape...all just by doing basic normie things and having normie hobbies. It seems so effortless, so of course the nerdy doughboy who has sedentary hobbies bashes them for being dumb sheeple who doesn't like the things they like,
Or that's how it used to be and now all the nerd shit is going mainstream and is being taken over by tards who have no respect for the hobbies.