They wrote the game targeting DX9, and then wrote a custom shim to translate from DX9 to OpenGL calls. Now they are transitioning to DX11 to get some newer feat

They wrote the game targeting DX9, and then wrote a custom shim to translate from DX9 to OpenGL calls. Now they are transitioning to DX11 to get some newer features, and have evaluated the amount of work that it would take to either update that shim layer for DX11 -> OpenGL/Vulcan for Linux, or DX11 -> Metal for MacOS (remember, Apple is depreciating OpenGL on their platforms). If linux and MacOS combine account for less than 0.3 percent of their revenues... then even as a MacOS guy I have to see their logic... there is little chance of recouping the heavy lift that they would have.