I think it has to do with the fun factor, or perhaps the usefulness. Cursing and insults tend to be the first things picked up by new speakers of a language. One of my first words in Japanese was baka ("idiot"). I amused myself endlessly coming up with funny insults in my Spanish class. no tienes nada quíche (you don't have any quiche).

This can be a good thing, since you've learned well the bad words so you'll be less likely to use them in an inappropriate spot. Then again, you may fall back on them if you're out of words and can't say anything else.

Another explaination is that most insulting words and phrases use a simple form of the language to make it easier to say or quicker. Many of the insults I've found in Japanese merely use the informal tone to say things like "you're an idiot" or similar. Since Japanese has (semi-)specific levels of formality, using a lower formality than is called for is insulting for the receiving party.

To also emphasize what TW related, I have found that I use the Japanese word "shitsurei" very often when driving and things are going wrong (due to traffic, no doubt). The word means "rude", but it sounds like the (English) swear word for feces. Other times, I'll use "Gotterdammerung", which sounds like "God damn it" rather than a part of Norse mythology. *shrug* humans are funny.