Much larger but not non-existent, people post their work (including laborious stuff like icon suites and themes) on art forums and websites for no gain all the time.
Going back to the winxp days there was a fairly vibrant group of people making unofficial themes for it, although I think that was helped by the existence of tools (from Stardock?) specialized on that task and making it approachable if your skill set didn't align perfectly.
