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.
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.
Then the choice is apparent.