The licensing.

Legally risky, too.

Unfortunately its implementation is spread through tons of hardware. Even my camera uses h265 for stills, as HEIF files, whereas not a single one I know of will do AVIFs or AV1 video (which is complex to implement as an ASIC).

One could say h265 takes the “easy” way to encode video, whereas AV1 (and presumably AV2) have to go out of their way and pursue complex alternatives to avoid patents.