Confession: I've been a professional software developer for 24 years, and I've never been able to get my foot in the door for an open-source project (other than my own open-sourced license stuff).

I think part of it is because the projects that are most worthwhile have no shortage of participants, so they don't need to extend any welcome to newcomers; and the projects that need participants often end up that way because they're not clearly good things to be working on in the first place.