Less commonly supported though, most notably by Apple and some TVs (quite import for that use case).
The whole video codec industry was predicated upon a particular licensing structure where everyone was paid to participate in ISO/ITU codec development in exchange for patent ownership over the final standard. That's why Apple never touched VP8/9 - decode blocks for ISO-standard codecs were very plentiful and very good, compared to those you could get for royalty-free Google ones.
Of course, nowadays the ISO/ITU business model is broken[0], so maybe the actual standards will move towards "royalty-free by default". Or AOM codecs will outcompete ISO ones and they become the de-facto standard[1]. But I don't see that happening until and unless Apple actually ships AV1 hardware codec blocks.
[0] Specifically, a good chunk of HEVC patents are only available from a company called Access Advance, a patent pool that has overlapping membership with MPEG-LA's pool. Since there's an overlap, you have to pay for certain parts of HEVC twice, and Access Advance won't reimburse you for the duplicate license. They say you should ask MPEG-LA for a reimbursement, despite the fact that said reimbursement would be more than you actually pay for MPEG-LA's half of HEVC.
[1] One of the founders of MPEG, Leonardo Chiariglione, is very outspoken that royalty-free codecs outcompeting FRAND codecs would mean the end of innovation in video coding. I personally find this a mistaken view (AOM's members were going to be doing the R&D anyway) but that's how the ISO/ITU people think.
"Proprietary" means "owned by somebody who restricts access". Access, in this case, refers to rights to run encoders, and to deliver decoders. VP8, VP9, and AV1 are also defined by published and recognized standards, but are additionally not subject to restrictions on use. This has nothing to do with money, and suggesting it does is disingenuous.
Also, do you get that Apple's reasons for anything they choose are at best obscure, where not actually fraudulent?
We all can only guess at Apple's reasons for anything, even where they seem to say what their reasons are, because Apple is under no obligation to reveal the whole truth about their reasons.
That Apple does not support VPx and AV1 is more reasonably guessed, from observation of historical behavior, to be a consequence of their preference for proprietary, exclusionary business models, most probably because they better limit competition.
