Because you haven't proven yourself to the GC overlords yet. Something about an arena battle and new member to-the-death battles... I don't know, you'll have to read up on in it the official forum rules. Regardless, welcome to the city, dude. (You need to rack up a few more posts before you can create threads outside of the noobie zone)
Typically noobs post really dumb threads so now there are restrictions on how soon you can start a thread after joining. Welcome to the city.
I'm actually so glad I found this thread because I'm pretty sure I'm too stoned to figure it out on my own >.>