And most of the standard we have now starts with something similar to NIH. Vulkan itself is an offshoot of mantel from AMD. There are valid reason to have a custom api. Especially in domain like game console with hardware with long release cycle, tight performance requirement and legacy (ps4) code to support.

Good, but if it's actually a standard - that's the benefit. If it's not - it's just NIH as in lock-in.