On a related note, why are release groups not putting out AV1 WEB-DLs? Most 4K stuff is h265 now but if AV1 is supplied without re-encoding surely that would be better?
Player compatibility. Netflix can use AV1 and send it to the devices that support it while sending H265 to those that don't. A release group puts out AV1 and a good chunk of users start avoiding their releases because they can't figure out why it doesn't play (or plays poorly).