> Youtube made it mandatory to have AV1 decoding in TVs/STBs for new devices since 2? 3? years, so it should become more common.

I think you mean Google, and they made it mandatory for Android. Most of those old devices don't use the latest Android version. And YouTube still happily delivers up VP9 to older versions as recently as two months ago.

> FWIW, on the vast majority of devices (well, all that I'm aware of), Mali isn't responsible for hardware video decoding.

If you're talking about LG, Samsung and Sony; yeah they have their own image processing hardware. That only applies if you're using the TV's app and not a settop device.

To clarify, I'm not claiming there are no AV1 devices or that it's particularly rare. Just stating that it's not ubiquitous enough to be made universal without a large segment of the populace/devices being affected.