For whatever reason, the file sharing community seems to strongly prefer H.265 to AV1. I am assuming that either the compression at a preferred quality, or the quality at preferred bitrates is marginally better than AV1, and that people who don't care about copyright also don't care about patents.
I assume "file sharing community" is the euphemism for "movie pirating community", but I apologize if I made the wrong assumption.
If that's a correct guess -- I think the biggest reason is about hardware support, actually. When you have pirated movies, where are you going to play it? TV. Your TV or TV box very likely has support for H265, but very few has AV1 support.
What is odd is that the power-seeders, the ones who actually re-encode, don't do both. You see H264 and H265 released alongside eachother. I'm surprised it doesn't go H265/AV1 at this point.
From a quick skim of hardware support on Wikipedia, it looks like encoding support for H.265 showed up in NVIDIA, AMD, et. al around 2015 whereas AV1 support didn't arrive until 2022.
So, the apparent preference could simply be 5+ years more time to do hardware-assisted transcoding.