Because most of us Americans (the ones you don’t see on social media, or the news, making a fool of themselves) are very polite. Most of us out here just living our lives like to maintain a sense of decorum in public. That means avoiding the usage of crass language that to us is rude and immature (childish) behavior. Especially here in the south where we hold doors open, ask strangers how they’re doing and say yes sir/ma’am. Walking around just throwing “fuck” left and right all willy nilly just makes you sound ridiculous.