My understanding of API standards that need to be implemented by multiple vendors is that there's a tradeoff between having something that's easy for the programmer to use and something that's easy for vendors to implement.

A big complaint I hear about OpenGL is that it has inconsistent behavior across drivers, which you could argue is because of the amount of driver code that needs to be written to support its high-level nature. A lower-level API can require less driver code to implement, effectively moving all of that complexity into the open source libraries that eventually get written to wrap it. As a graphics programmer you can then just vendor one of those libraries and win better cross-platform support for free.

For example: I've never used Vulkan personally, but I still benefit from it in my OpenGL programs thanks to ANGLE.