Talk:Characters/@comment-25531876-20150220143235/@comment-4531340-20150223030204

It's probably because the background characters are just usually there as filler, and so are a blank slate, personality-wise, so the fandom assigns various personalities to them, some of which become more popular than others (and some bg ponies, like Derpy, Vinyl, or Octavia, become more popular than others). Then, when they show up more and more in the background, or even have a few lines, it's kind of exciting, almost like a substitute for getting fan OCs in the show (since the creators have said that's never gonna happen). At least, that's what I think is the reason.