I understand why a lot of people don't. Swearing is often a crutch for the uncreative, and a lot of people realize that. To use it effectively takes talent, and to use it ineffectively can be pretty damaging, so most people are probably better off just leaving it alone. Someone like Bill Cosby can be thought of as a far better comedian than he really is simply for not using it.

I have a feeling that if I were a better programmer I could come up with a great analogy here, but alas, I'm a hack.