Because you did not do the tests BEFORE buying your card. I simply do not get why people still do not TEST what is limiting on their CURRENT setup, before running out and buy new hardware. Especially with todays features like DSR and RSR, it is so easy to know with a single session if replacing your GPU will provide you any benefit or not.
Means: if you are so CPU limited as I guess, DLSS will provide you nothing. Not. a. single. FPS. more. Why? Because if your CPU is only capable of delivering 20FPS, it will be 20FPS no matter if you use DLSS or not.
So, all you can do is lower those CPU heavy settings like terrain and object LOD…