The current engine probably doesn’t come close to supporting it. They’d need to do a significant upgrade for something a tiny fraction of the base could take advantage of, and since Bungie won’t just migrate to UE5 it would take well over a year of engineering and development time to do it. And the end result will probably break the game and make Elden Ring’s RTX implementation look ambitious.

1) Laziness 2) Old hardware (XB1/PS4) 3) The game notoriously is held together with duct tape and a dream 4) Out of the box Lighting is historically a strong suit of Bungie's

Because a polished turd is still a turd.