The core engine is old. Realllly old. It’s essentially the halo engine they used for reach and such. Most of the destiny 2 updates have been more on the quality of life stuff or texture rez. And it’s so problematic that not only do they have to remove maps and content so the engine functions, but they run into memory issues with too many mods. Could be it’s too old and spaghetti to get dlss added As many problems I have with Epic, they make large changes to their engines infrastructure over time to keep it modern and incorporate new tech. Though they license their engine so that could be why.

Dlss only works with some nvidia graphics cards which I am sure that no xbox one/ps4/xbox series s/x box series x/ ps5 or most lower to mid range pc's have. So a feature for a small percentage of players is probably not a high priority.