Because vB has it out for us and we're not fat rich corporate dogs so we can't feed them cash. However, I have xenForo paid for as well as IPB so it only makes sense to use one or the other.
Apologize if it's hard on your eyes right now. The only skin you see here that will stay is the Konata skin. I'm in the process of adding a dark skin. Hopefully you'll like it more. Off course the forum functions differently so you'll have to adjust a bit, give it some time and I think you'll like it.