It seems inevitable to me that Google is going to shut down Google Groups or else fold it into Google+ in some unpleasant way. Maybe when that free option is taken off the table there will be more room for a commercial solution.
Whatever reasons there might be for why forums/discussions aren't getting any better, the existence of Google Groups is not one of them.
By the way, Google Groups used to have a great UI but over the last fre years they've changed around the design and it is horrible now.