DirectX 9 is long term stable so I don't see the issue...

No current gen console supports it. Mac is stuck on OpenGL 4.1 (you can't even compile anything OpenGL on a Mac without hacks). Devices like Android run Vulkan more and more and are sunsetting OpenGLES. No, OpenGL is dead. Vulkan/Metal/NVN/DX12/WebGPU are the current.

The aforementioned abstraction layers exist. You had dismissed those as only suitable for backporting. Can you justify that? What exactly is wrong with using a long term stable API whether via the native driver or an abstraction layer?

Edit: By the same logic you could argue that C89 is dead for new projects but that's obviously not true. C89 is eternal and so is OpenGL now that we've got decent hardware independent implementations.