Reddit is great for the specialized sharing of content. If you want to see the latest videos, or cat pictures, or read Seinfeld fan fiction, theres a subreddit for it. The problem is that it doesn't allow for great discussion between users without messages being hidden behind the most upvoted and gilded posts. The competition puts users at each other's throats instead of having actual discussion. Hubski is such a brilliant platform because it prioritizes thoughtful discussion above anything else.
And the motivations that come with karma don't help across the whole of Reddit. If you write a stupid one-liner in a default sub, it's an easy way to get thousands of points. If you write a valuable, in-depth discussion in some niche sub, you're lucky to get a dozen points.