I agree with the OP, I'm not that concerned with the reward since as far as I know we only get 1 roulette per day. I am more interested in increasing the variety of dungeons I can do as well as helping out some new players. I usually pick up 1 or 2 friends and one of us is always a tank/healer simply to improve queue times. In my case, since we can't join roulette in a group of 2 or 3, it would decrease the number of tanks/healers because we will do something else that does allow parties.

That said, they have announced that it will become available in 2.2 so that makes me think they're having a technical issue that needs to be resolved since they're clearly planning to add the feature. Perhaps they want to monitor server loads without parties involved so that they don't have a repeat of launch issues? They're also increasing the number of available dungeons in 2.1 which will help tide me over in terms of variety until then.