Apple supports formats they can hardware accelerate. They have historically picked one format to accelerate in hardware (H.264, now its HEVC), and pay the royalties with the format they pick.
Apple SoCs have VP9 hardware acceleration support already and they still won't support them to push HEVC.
Also there's no reason for them not to HW accelerate WebP with the same system (the frames are compatible) but they chose not to, so I'm not quite sure what your point here is.
Also there's no reason for them not to HW accelerate WebP with the same system (the frames are compatible) but they chose not to, so I'm not quite sure what your point here is.