Extensions are the stick with which hardware vendors beat platform companies (in practice, Microsoft) into innovation. That's how we got raytracing, for example.
Hardware raytracing was designed by NVidia and Microsoft together while creating DirectX 12 Ultimate, shown to the world in an Unreal engine based demo of a starwars lift scene, it has zero to do with Vulkan.
I doubt either of us were in the relevant rooms, but the API is very obviously a DX-ification of Nvidia's OptiX (the software-based raytracing solution that they released long before HW raytracing). Furthermore, Nvidia released OpenGL and Vulkan extensions for raytracing long before the release of DX12 Ultimate. Do you think Microsoft would have allowed that if it was a genuine co-development by the two companies?
With extension spaghetti, not only are we back in GLAD and GLEW land, each set of extensions is yet another possible code path.