How many of these used Facebook, Twitter or Reddit? They are not mentioned in mainstream media because they are popular, but I assure you there are a lot of deranged people that never even posted on 4chan and just stuck to the “good” ones.
Yeah I don't think the 4chan demographic is substantially different from the "normie" social media. It's just that everyone speaks more openly about what they already believe there, including the crazies.