I listed a few: freedom, time and indulgence. More specifically, the freedom to pursue passion in life is often enabled by one's parents having enough money and stability. Time is mostly about leisure time. Having a job that supports work on open source is still not that common, so one is left with figuring out how to do this on your own time - and that depends on you actually having free time because you don't have kids, you only have one job, and you have the background knowledge (socially, tools-wise and background reading) necessary to participate.
So, that's how the whole world works, right? I am not saying that Postgres is unique here. I think we actually do a really great job. We have about 300 contributors every year, and only about 20 committers. That's impressive and shows how the contributors feel about our project. It is prestigious, interesting and fun enough for them to send us their code even though we don't give out commit access, and we subject everyone to a pretty difficult code review.
That just goes to show that if you ask a lot from people, they like it and come back for more. Or at least the people I want to be in a community with like it. :)
I am bringing up to my community that we could do a little better inside of Postgres. We could take a closer look at how we operate, and find ways of inviting people in that don't already fit our mold.
There isn't an easy solution to addressing privilege inside a community, at all. But I was at a conference last week, and a couple people asked me to write my thoughts down about meritocracy. It was not an easy thing for me to do.. I already see a few de-railing comments about gender.
But I continue to get support for thinking and writing about this issue, and ultimately finding more ways of getting more contributors. This is why I continue to contribute, and why I took a moment to make a gentle criticism of a community that I enjoy very much.