Honestly, the majority of bullies are usually guys who have little actual contact with women generally. The nature of online gaming is a social outlet. Now, more than ever, people use online gaming as a way to connect with like-minded people. Not all, but some, don't know how to properly function in a real life social atmosphere, and resort to going online as their looks, personality, and finances are easily hidden. As is common in even forums like .NET, you see more and more people say absolutely ridiculous things due to anonymity. Being polite, mature, and respectful are slowly going the way of the buffalo in an age where there are no repercussions for their actions.
Quite simply put, human nature is at work here. The biggest man in the tribe makes the rules, and no sane man shall cross him.
There is no "The Biggest Man" in an online world. There is nobody to step up and beat some sense into these idiots.