Then find these bands that you're interested in.
Look them up on Wikipedia or Myspace. Find out what label they are on, then contact the label and tell them how much you'd love for that band to be in Rock Band Network.
Simple as that.
If enough people are talking to the labels about said band being in the game they'll more than likely look into it and see if it's a worth while venture for them.
Beats complaining about it to people that can't do anything to help, amiright?