> The decision not to support Vulkan however is most likely a political decision.
The only platform where running WebGL on top of Vulkan would make sense is Linux, and on Linux both the GL and Vulkan drivers are in good shape via the MESA project (e.g. there's little incentive to switch from a perfectly fine OpenGL driver to Vulkan for implementing WebGL), especially since the only outlier (NVIDIA) doesn't have all that great 'native' Vulkan support either (IME at least).
The only platform where running WebGL on top of Vulkan would make sense is Linux, and on Linux both the GL and Vulkan drivers are in good shape via the MESA project (e.g. there's little incentive to switch from a perfectly fine OpenGL driver to Vulkan for implementing WebGL), especially since the only outlier (NVIDIA) doesn't have all that great 'native' Vulkan support either (IME at least).