The problem is that vulkan was specifically designed to throw away an amount of portability in favour of allowing lower level access to hardware features. If said hardware features don't exist on a platform, you're stuck. Note the "The Vulkan Portable Subset" having to throw away a number of features to have it work on a number of underlying platforms https://www.khronos.org/vulkan/portability-initiative .

The advantage that opengl has is a number of software implementations that can be used as a last ditch on unsupported systems. Efforts for software vulkan implementations are taking a long time to appear.