Because Vulkan gets them Android and Switch support. They aren't insignificant enough markets to just ignore. I think Sony said at some point they wanted to su

Because Vulkan gets them Android and Switch support. They aren't insignificant enough markets to just ignore. I think Sony said at some point they wanted to support Vulkan on the PS4 as well, but that never precipitated. You can use Vulkan on the PS4 GPU if you homebrew Linux on it, but thats not quite what developers are interested in.