Two key points for me (my emphasis)
The reason is that the power of the major sites comes from combining large-scale contributions from heterogeneous participants, with heterogeneous motivations. Pointing to the 80/20 rule on contributions misses the dynamic that comes from being part of a large community and a recognized leader or major contributors in it, for those at the top, and misses the importance of framing this as a non-priced social process. Adding money alters the overall relationship. It makes some people "professionals," and renders other participants, "suckers."
There is an abiding skepticism, born of many years in the industrial age, about the sustainability and plausibility of nonmarket-based cooperation and productive collaboration. We have now, on the other hand, almost two decades of literature in experimental economics, game theory, anthropology, political science field studies, that shows that cooperation in fact does happen much more often than the standard economics textbooks predict, and that under certain structural conditions non-price-based production is extraordinarily robust.