[TheGuyWhoCodes]

Reason are unknown but there are speculation. https://www.youtube.com/watch?v=nIoZB-cnjc0

This is a very good explanation/speculation which deals with the NV driver optimization for DX11 where they break up the draw calls between threads because the scheduler is software based where AMD is hardware based and can't do the same. In DX12 this isn't needed so AMD scheduler being hardware based can be better utilized.