Vulkan, as a Khronos open standard, likely wouldn't exist if Apple didn't make Metal. Khronos was content for OpenGL{ES} to sputter ad infinitum until it realized that its largest platform (iOS/macOS) was moving on. It helped that the rest of the industry (MS, AMD) was also moving in the same direction, but it was the release of Metal that broke the camel's back.

There were several efforts in the past to revamp OpenGL (e.g. long's peak), but they all failed. OpenGL was stuck and there was little reason to think the situation would improve. Writing OpenGL code that worked across multiple platforms was worse than it is today to write multiple per-graphics-API render backends.