As it happens, OpenGL was so high level that supporting it on top of DirectX was feasible. A number of Windows browsers use the DirectX back end to ANGLE, so users don't have to download OpenGL drives.
Unfortunately, that doesn't work as well for Vulkan. Vulkan is the lowest-level of the three APIs, so it's hard to support on top of Metal or DirectX 12.
Re:Apple proposes new web 3D graphics API
by modeless on Tuesday February 07, 2017 @07:42PM
(#13594554)
Since WebGL was released, Microsoft has demonstrated a new willingness to support Web graphics. They joined Khronos, and now ship a WebGL implementation of their own with Windows. I have confidence that if the industry moved toward a WebVulkan standard that this new Microsoft would make platform changes to better support it. Unfortunately I have no such confidence about Apple.
Why don't you ask Microsoft what they think about this proposal instead of speculating?
This is not materially different than the situation with OpenGL, and yet I hope you'll agree that basing WebGL on OpenGL was the right decision, rather than inventing a new API based largely on a lower level API proprietary to a single company's platforms.