>>545820337
Because bungie used a closed source proprietary audio codec that was heavily modified to run on a 360.

>Reach has some challenging technical hurdles - the foremost being the update and transfer of the audio signal path and processing scheme from the original release on Xbox 360. Since the underlying hardware architecture of the Xbox 360 is fundamentally different than our current Xbox One and PC platforms, our first internal pass involved an approximation of the PowerPC audio code and DSP.

Not only that but those tools are outdated as fuck and were never updated, I believe they were already outdated by the time Reach was released.