For the same reason people do Burning Man. To learn and grow. And to form a community that values creative learning and growing.
The temporal nature of it is vital to having immediate and unmediated experience, and the DIY aesthetic meshes perfectly with Second Life's riot of user-created content. When Philip Linden put the tools of creation into the hands of Residents, he set up the same level playing field that energizes Burning Man.
Everyone contributes. Nobody is special, and everyone is a star! So get involved. It doesn't even matter how much you know about Second Life.
If you are not a great builder-- this is the place to experiment and learn from others.
If you don't know anyone in Second Life yet, you will. If you are a veteran of Second Life and you crave a little good-old-fashioned creative chaos, come on out.
BURN2 will be exactly what each of us put into it.