The belief is 5 v 5 isn't a competitive bracket. It's only for points and can be exploited etc. That's why it has no rewards and isn't taken seriously.

Solo Queue on the other hand is taking up the arena slot, is given the quests, and has incentives.

So why not combine the two for TBC? Making Solo Queue a 5 v 5 game would strongly appeal to players wanting points and greatly increase activity, encourage other classes to play, and where 5 v 5 wasn't coordinated hardly anyways then it would fit right in. It might be nice not having to maintain a 5 player roster too.

I think it's a fair compromise.