While true this boils down to "Apple won't support anything it doesn't have control over", as demonstrated by them using veto power to pick WebGPU's shader language (a custom one) instead of using the shader IR literally everyone else wanted. It doesn't make a ton of sense to evaluate the success of APIs and standards this way because Apple has a long track record of refusing to implement stuff or deprecating it once they had an interest in promoting a proprietary alternative.