Multiple times. You should try watching some of the Q&A sessions. It was on the dev roadmap for “summer 2021” many months, which was likely intended to be SU5 and with the Xbox release (it’s already on DX12). But my guess is that they didn’t get it done in time. Likely SU6 inSeptember will see DX12.
It’s right there…
PS: This isn’t the “wishlist”. This is the actual dev roadmap of what IS coming.