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).
??? For example, there are a substantial number of emulators that have already implemented or are in the middle of implementing a Vulkan backend: RPCS3, Dolphin, Yuzu, Cemu, Ryujinx, PPSSPP... these emulators are developed by small teams but often push the hardware hard, bringing bugs to light in the process.
There's always going to be a balance point, and Vulkan's priority is much more about getting as low-level as possible within the constraints than it is about being approachable for developers.
Doesn't khronos contain people from a bunch of different corps (amd, nvidia, intel, qualcom) for this exact reason.
And how else do you propose accessing hardware features which are vendor specific?
Isn't this why Vulkan was designed the way it was. It's lower level, giving more control to things like memory. In this way I view it somewhat like the ASM of the GPU (even though though there are lower levels still).
I'm curious if anyone with a lot of experience writing graphics "middleware engine" backends agrees.