You can expect this to continue happening for as long as Apple pushes Metal and refuses to support Vulkan. People are not going to design desktop class games around API that has single platform use. Blizzard did the same thing, with dropping macOS support in their newest titles, although they for now keep the old ones working. If macOS wants to get anywhere is desktop game support it has to be a case "why not support it" instead of "we need to make a Metal compatible version of our engine".
Just adding support for Vulkan won’t be the solution either.