OpenCL didn't seem to be succeeding, so that's not entirely surprising. It is disappointing that they've chosen to deprecate OpenGL and ignore Vulcan in favor of Metal, though. Although I don't know much about this particular area, and I couldn't tell you about the merits of Vulcan vs Metal. It's hard to tell whether there's any good technical reasons for their decisions or if it's purely just business in that they don't want to contribute their resources to something that will benefit Android.
Admittedly, I am also not well versed in this area. My guess is, because Metal is proprietary, they can include intimate details of their hardware platform to squeeze out the most performance. And they probably would not feel comfortable having that same level of detail in Vulcan.
