I think it comes from modern mass media technology. If musician A is better than B there is little reason to listen to B, unless you live in 1600 and musician A works in the next town over.
Modern mass media cannot generally differentiate between A and B because there are zillions of indistinguishable musicians invading the attention of people with very different marketing capacities.
Nah, it existed when barrier to entry was much, much higher. What causes it is the fact that with recording and copying technology, creative work scales extremely well, especially with positive feedback effects of popularity and marketing. This is what creates the very small number of very high earners. If anything, the lower barriers to entry (especially with regards to being able to distribute your work) have flattened the curve a little bit, as the long tail of obscure artists is longer and thicker than ever (and the shape is the same: each obscure genre/subculture has a few artists doing very compared to the others, though it also flattens off once you're looking at artists who primarily make money from commission work, as that doesn't scale nearly as much).
There's probably some truth to that. You either have gatekeepers or a huge number of people just fail. (Even with gatekeepers a lot of people just fail anyway but but of people just don't get the opportunity to participate--which may or may not be efficient.)
