Online dating is much like the kind of party where there is only one girl, but tons of guys and no matter what that girl looks like she gets a lot of attention. The odds are most men on those sites send a message to practically every girl who is reasonably good looking, you know playing the odds, and because of this it makes the girl develop a bit of an ego.
You can pretty much guarantee that if you have decided to send a girl a message that tons of others guys have as well, therefore it makes them believe they are better looking than they once thought.
Not many girls will bother sending a message out because once they have registered on a site the guys will have pounced within a few minutes.
I don't understand why music makes much of a difference though. I like metal too, but it hasn't gotten in the way of meeting girls. Unless of course you are dressed up with metal spikes and chains. Are you?