Actually, I think there's a very good reason for this. Largely, I think yoga helps people to stop defining themselves by some set of expectations, by how they would like to be perceived by others, for example. In place of these external definitions, there comes a sense of contentment and confidence. The student expresses this point quite well: "Yoga clears the clutter." For whatever reason, asana practice has helped me be clearer about priorities, and how unimportant are so many little worrisome things. I think the clearing of clutter goes hand in hand with the increased contentment and confidence I mentioned before.
And I think that Gates is right that this all stems from being honest, from dropping pretense. By practicing honesty on the mat, we come to learn that that honesty is enough, and also that it works. Not only that, it works better than either pushing too hard, or lying to ourselves that we won't ever be able to do anything. Since honesty on the mat does work, it tends to breed confidence and a sense of satisfaction. And that confidence, that sense of clarity, clears the clutter. Then, since we find that being honest with ourselves works so well on the mat, it becomes tempting to try the same experiment off the mat. And the results there can be at least as astonishing.