I'd like to believe any developer has more than a few pet projects around which they dedicate their time into whenever one has free time. Some get forgotten, others are overly specific to be marketed at all but maybe that one in a hundred has the opportunity to become a good investment, so it is just matter of buckling up and trying to ship it to the world. This doesn't mean it's going to make you financially successful, but actually delivering products does give you the experience of knowing what makes a successful one if anything at all. If you are lucky, you may break even in terms of time/resources spent after all the ordeal and you also get experience, though I wouldn't say that's the experience of most for the first few times, there's always a point in trying.