Not tottally agreeing with Blaq´s reason,
i beleive that communication of some form or another, is a crucial major primary basic need of the human kind. makin somekinda contact with a fellow earthling to voice/exchange ideas, spread a message, soak up some info, debate an issue, talk weather n yeah even sometime just clown around wich for some reason seems naturally essential to our psyche well being
that´s why we invent such means as Phones, Radio, TV n Internet connections.
n since internet interacting seems to encourage one´s anonymousness, n much unlike other forms of media (like phones n TV) nothin off u is really heard or seen. n on top of that one is provided with the cool options of hookin up a nickname of choice (avatars n shit) all contributing to the ease with wich one can feel tempted to explore n get in touch with an extreme side of his personality he wouldn´t normally explicitely show in everyday life
Peace