It's not. It's an ENTERPRISE theme music. Why do you think they drop Star Trek from its title? Everything in that show is before the Federation, when Starfleet was a fledgling Earth-based organization.
If you think that TOS is the "Wild West" version of Star Trek, then ENT is the "Dark Age" version.
Personally, I like the rock tone of the music. It is Earth-based rather than being part of something larger, like the soon-to-be Unifted Federation of Planets. Plus, Rock-n-Roll have always been criticized as rebel music, not as sophisticated as Jazz or Classical. It's about time Rock-n-Roll get some more exposure in Trek despite Star Trek IV (punk rock music on the bus) and Star Trek: First Contact (50's hillbilly rock music in the jukebox).