As for waht keeps Metal underground:
The general population of this planet are sheep that WANT to be told what to think, and want simple things... well, it doesn't get much simpler than pop music! Not to mention it's way cheaper for record companies to "discover" and push that crap out the door. All they need is a pretty face, and the ability to lip-synch and dance and not argue with the company execs... Metalheads are notorious for having artistic integrity, writing their own material, playing their own instruments, and will fight to have what THEY want put out there... that's a headache for the labels. Not to mention, that most good metal is actually thought provoking... the masses don't like that!
Cheers!