The dust settled on these accessibility features years ago. Why would Apple choose not to do these things? Live captions in particular is useful even for those who are not hard of hearing because it lets people watch uncaptioned videos in environments that are too noisy or that need to be quiet.

By "dust settled" I don't mean that the technology "exists" -- but rather that feature development has slowed down and most products have stabilized as feature complete and mature.

The on-device ML models that are being used by Google and Apple are both quite new and in active development.

Many of Apple's most successful products have shipped years or even a decade after their competitors. They have tried using first-mover advantage in the past but typically fail when using that strategy.