On the webGL/GPU side, my cynical speculation is that the Apple has slowly been amassing a nest of graphics talent for the last 5 years (Metal, Vision Pro, ARKit, list goes on), and at this point they can't resist the pressure from employees to not support some of this stuff which should be table stakes and is obviously good for the user experience.
On the PWA side, best guess is anti-competition scrutiny.
On the PWA side, best guess is anti-competition scrutiny.