The reality is, in house tooling and engines do use multiple graphics api's, and that's perfectly fine. They are not slapdash implementations; professional graphics rendering programmers know and use these API's (See the GPU Pro book series, and Real Time Rendering), it's their profession.

A commercially successful multi-platform game like skyrim, use at least 4 API's (DirectX, NVN, PSGL, and DirectX), but no OpenGL or Vulkan to be seen at all.

Anvil and Frostbite have no existing opengl driven software titles. And that's perfectly fine.