Because has better texture detail? Others have made YT videos comparing the image quality between AMD and Nvidia. As recent as comparing RIS to DLSS.
If the GPU renders lower quality textures ofc is faster.
I reported that when after 2 1/2 years moved from 1080Ti (and 1080 before that) to Vega 64, and in comparison to my laptop 1060 6GB. The game playing several hours per day (WOT), over the last 9 years, looked so much different, on same settings. Sure went from 150fps to 110fps but everything looked better, and wasn't the gamma some say. Grass details, bushes, trees were more lush and had more foliage, water and mirrors had reflections never saw before. Sure the extra bush foliage this is hampering my ability to shoot from behind double bushes (something was used to do), but I prefer the current image quality more making it feel proper game.