They only care about standards when they're basically forced to adopt/support them, or they're their own.
These are the same guys that:
- use lightning instead of mini USB
- removed the headphone jack
- are creating yet another proprietary connector for accessories
- don't allow their OS on third-party hardware
- only allow developing for iOS from macOS
- only allow apps on iOS if you install from the App Store
- only allow their own browser engine on iOS
- etc.
Everyone wants their own standard to be the standard, if they really cared about it they would contribute to Vulkan and create WebVulkan.