Hegemonic (i.e., WASP) US culture is very much "swearing is uncouth." Which is a problem not only for non-USAmericans, but also for e.g. Black Americans speaking in US white-centered spaces (like much of Mastodon). Like Jyoti said below - cultural hegemony.
The absolute *worst* is when white people get offended when Black people say "nigga." I have never wanted to kick a motherfucker in the chest as much as I do when that happens.