HW support for av1 is still behind h265. There's a lot of 5-10 year old hw that can play h265 but not av1. Second, there is also a split bw Dovi and HDR(+). Is av1 + Dovi a thing? Blu rays are obviously h265. Overall, h265 is the common denominator for all UHD content.

I avoid av1 downloads when possible because I don’t want to have to figure out how to disable film grain synthesis and then deal with whatever damage that causes to apparent quality on a video that was encoded with it in mind. Like I just don’t want any encoding that supports that, if I can stay away from it.

Encoding my 40TB library to AV1 with software encoding without losing quality would take more then a year of not multiple years, consume lots of power while doing this, to save a little bit of storage. Granted, after a year of non stop encoding I would save a few TB of space. But it think it is cheaper to buy a new 20TB hard drive than the electricity used for the encoding.