The "ladies' night" strategy
cdixon.org
cdixon.org
To contrast, Amazon seems to have done a good job of growing out its base of satisfied external sellers (no personal experience, just anectodal). Perhaps aiding this is the fact that Amazon has an intimate understanding of how to succeed as a seller (they get fulfillment, pain points in the purchasing process, etc.). They worked to cultivate their main market (the buyers), while actively operating in their future market (as a seller).
But if you get a bunch of the easy side, that will attract the hard side. You can do it either way.
Look at buyers and sellers. If you have tons of buyers, that will attract sellers. And if you have tons of sellers but no buyers, that will attract buyers.
What percentage of Windows users chose Windows "because there are so many developers"? (I'm sure many developers develop for Windows because of the vast number of users.)
also back in the 80s/90s app availability was a huge battleground for OSs, and became a big advantage for windows over OS/2 etc.
The difference between Wikipedia and Reddit/HN is what I would venture calling 'contribution barrier.'
Think how hard is it to contribute to a Wikipedia article vs. Posting or commenting on Reddit/HN. Let alone voting.
I'd imagine that most of the registered users have voted, and a majority have commented. I don't imagine quite a lot of people have posted links.
If I'd have to guess a ratio of lurkers:voters:commenters:posters, I'd say it's 40:30:25:5.
Do you have more great suggested resources to read?