[johnnyanmac]

Job pays them really well and/or they are very well off already, so a minority have the time and passion to try and make something on the side. Even then, the biggest and highest value OSS have full time maintainers and offer pay for that. Are there really any Linuxes out there that were purely maintained by free labor?

Alternatively, students who want portfolio pieces. They have an incentive to stand out in a job market and make money as an endgoal.