Apple is a "Founding Member" of Alliance for Open Media (which doesn't really mean they are actually a founding member). I think Apple main issues with VP9 was that it was a Google codec by all means.
Apple already supports FLAC and Opus in macOS and iOS, and VP9 in Safari.
It could be that they are waiting to see if AV1 will actually get a marketshare outside Youtube or not.
...to bad that they (in the usual Apple fashion) don't support it in a standard container which everyone else supports and require you to package it in their special snowflake .caf container, so even though in theory everyone supports Opus you still need to use MP3 if you don't want to deal with having to support multiple formats/codecs at the same time.
VP9 is an open format but can still be encumbered by patents. $20 says Google gave Apple an indemnity agreement for VP9 support for YouTube only which is why VP9 is locked down so hard in iOS. So if Apple enables VP9 and gets sued for patent infringement for their VP9 implementation Google will have to pay for some or all of the legal costs and/or judgements resulting from them.
I'd say they are, but the real issue to Apple is how this or that format will affect their users and how it will portray their products. That is, whether or not they can decode the format without the device running hot, noisy and out of battery in 45 minutes. They like H.264/H.265 because users can decode them with high power-efficiency due to GPU- and dedicated hardware support. This is one of the greater benefits of formats that the whole world accepts and adopts.