That presumes that either (a) they have time to spend doing substantial work with open source outside of their day job and other obligations, or (b) they have a

That presumes that either (a) they have time to spend doing substantial work with open source outside of their day job and other obligations, or (b) they have a day job which allows them both the time and the regulatory freedom to contribute to open source. For many programmers with the desire to contribute to open source and substantial work experience, this is not the case.