I believe it is the democratization of music. Hatsune Miku songs are written and produced by fans. You don’t need to be able to sing, or record instruments. Everyone can join.
From Wikipedia:
> In August 2010, over 22,000 original songs had been written under the name Hatsune Miku. Later reports confirmed that she had 100,000 songs in 2011 to her name.
It's Nico Nico Douga/nicovideo.jp. There is a unique community and reward mechanism that values technical achievements far more than it does for presentation, and that I think is forcing creators to go way past in skills than what YouTube and many other social media demands. That culture comes as an extension to Japanese anonymous BBS(2ch/futaba), and I find content from those communities to bear abnormally better quality compared to those from the Internet outside.
I can walk into Walmart, FYE or Hot Topic and walk out with Hatsune Miku merchandise. You can't even say that for many popular anime franchises (only stuff like Naruto or Dragonball that's been popular for decades). I've even been to small fan run projection concerts.
Vocaloid music has a huge following in the US. It's just a subculture thing and not part of the mainstream sphere...which is a good thing.
From Wikipedia:
> In August 2010, over 22,000 original songs had been written under the name Hatsune Miku. Later reports confirmed that she had 100,000 songs in 2011 to her name.