I would say there are two important facts here:
1) Bungie's main claim to fame is tailoring FPSes for the bro crowd. That is after all why the tea-bag became the official victory dance of bros everywhere with Halo at the helm.
2) Bros don't really need a well orchestrated score to simulate the act of homoerotic violation of corpses. Unce Unce Unce will do just fine.
Seems to me someone just woke up and put one and two together. Seems to me a sweeping score would just make bros feel uncomfortable when they are pretending to rub their groins against the gore and blood filled mess of what used to be a dude's face. They wouldn't want the experience to suddenly become 'gay' now would they?
Outstanding post lol