What happened is that Khronos Group banked on third parties writing OpenGL-esque "middleware libraries" that bridged the gap between the hopelessly complex Vulkan API and people who want to write simple 3D graphics. Unfortunately, Khronos learnt the hard way that you can't just expect people to do work for you without a sufficient incentive, since after all, OpenGL still exists for anyone who wishes to have an easy API for graphics programming, and anyone who doesn't want to do that just uses an engine or high-level graphics API.

Of course I'm not saying that these libraries don't exist, but they haven't taken off in the way they expected