When you ask developers who maintain OSS projects why they do it, a common answer is the gratification from seeing so many people using your code. It's the same feeling that an author gets when someone has enjoyed his book or a artist feels when someone enjoys their painting. Most software developers liken their work to artistry and most take great pride in it--they enjoy being recognized for contributing to the field. For those people, OSS is the most effective way to ensure that their code reaches the maximum number of people.