I would also add, the ability to spread things by word of mouth online is much better in the age of social networks etc. So even very obscure niches can get filled.

For example, so far as I can tell, these guys have gotten most of those likes from reshares of the video (I've seen it several times, from completely random people). Whereas if you did market research, I doubt that "Mongolian bluegrass folk" would rate highly, so finding a publisher might get tricky.

https://www.youtube.com/watch?v=jM8dCGIm6yc