Simple reasoning.

They say what they hear, and curses aren’t a huge deal in other places. It also may have been translated.

The bad thing is making them known as curses. Such words are offensive because people say they are offensive. You can see this in America quite easily. Very few people under the age of thirty see words like "Fuck" or "Shit" to be curses. They use them like normal words so nobody cares. Older people remember when they WERE insults and curses, so they are insulting. It's a fascinating evolution in language and what makes it even more interesting with this generation is that we haven't created any replacement curses. Our generation has no curse words and I find that fascinating.