Have you ever wondered why you don’t find job advertisements for “user experience developers”? For that matter, why do designers monopolize improving the experience of users? It is not like designers are the only people who impact the user experience. After all, the user experience is not the same thing as the user interface. The user’s experience is affected by many things beyond the interface.
In fact, although I am a user experience designer myself, I would argue that in many ways a developer has a more significant impact on the user experience than I do.