Also some of you people seem to forget that the RBN is not something HMX is running and doesn't have the same resources or influence to even get huge artists most of the time. The fact that some big names like Steve Vai, Evanecence, Mastadon, Eifel65 and those 80's hit artists are on the platform at all is pretty amazing. Trust me, if I had the possibility to do so I would have gotten Muse on the RBN, but thing is that is just impossible to do.
Also the whole point of the RBN is to allow lesser known artists to have a chance to get their songs into the game that HMX would never pick up as official DLC and to create a big market with a lot of choice for the customers between the big hits on official and underground and niche stuff with the occasional big name guest star on RBN.
I think the reason so many Metal artists get onto the RBN is a mix between the bigger authoring groups getting exclusive deals with record labels and want to make as much out of it as possible and that a lot of up and coming Metal bands have a hard time getting promotion and RBN working very well for that.