The reason being to have a central place to go for forum posts. Reddit is the king of forums, and has a lot of easy to use tools to enable forum management and things like the Diku WIKI. You can also design your own template to match the look and feel of colors, handles, post layouts, etc. Better search capabilities, easier tools to create subforums for topics and junk. Forum control can be spread amongst the moderators without needing to ping Gabe with things like 'the forum is down' or 'Krilcov is at it again and DDOS'ing us'

The only real con that I can see is Gabe loses out on ad revenue from the banner ads and Google integration in the site. Then again, bye bye hosting fees.

Why not move to Reddit?