H264 seems to still be the preferred codec in this space, even though H265 is a smaller file size.
Largely due to the CPU over head of H265, though I am not sure why more people do not use GPU encoding over CPU Encoding, I have never been able to notice the difference visually
From what I can tell from a cursory look at some popular tv show torrents, everything 1080p and below is still h.264, with everything above that running on h.265
Nvidia's NVENC doesn't support CRF, one of the more popular methods of rate control during encoding.
NVENC is too low quality for the scene.
Not for 4K rips. I see tons of x265 10 bit encodes, just look for UHD or 2160p copies.