I don't think even Nintendo knows why they do or don't do anything :p
It's definitely a feature they should work on. My personal interest in them is pretty limited, but I've always thought it was a great feature. I've seen hundreds of people on PSN, XBL and Steam that enjoy collecting achievements, while only a handful that actively dislike them. Those that don't care either way just ignore them. Seems like a win-win in my books.