The idea was probably "built it and they will come" (the library authors who provide the easier to use wrapper libraries). The problem is that these libraries are hobbyist/volunteer work (with the notable exception of native WebGPU implementations), which on its own isn't a bad thing, but hobbyist can't afford a testing lab running hundreds of GPU/driver/OS combinations to make sure that their libraries are as robust as expected.

The companies who have these resources (for instance the GPU vendors), chickened out by designing Vulkan and thus offloading those QA tasks to the API users (simplified, but that's what it is in the end).

Which leaves Unity, Epic, and a handful AAA game developers as potential Vulkan users, which in turn are not enough to test Vulkan implementations, because just a handful API users isn't enough to cover all the dusty corners (same situation as back in the bad old days with MiniGL).