Why RADV requires AMDGPU and doesn't support Radeon?

Vulkan is supposed to work on GPUs that support OpenGL ES 3.1 or OpenGL 4.x and up, so why RADV doesn't work on pre-GCN cards and GCN 1.0 and 1.1 cards that use Radeon instead of AMDGPU driver? Do you think of people running old hardware and not having money and/or reasons to buy new one? What about people running *BSD where AMDGPU is either not present or buggy? What about people hating AMDGPU and preferring Radeon instead? Basically Vulkan is about lowering the gaming audience.