The things being emulated are mostly legacy features that are barely used in modern software, if at all, so the overhead of emulating them for backward compatibility isn't the end of the world. I can't blame Apple for not supporting geometry shaders in hardware, when they're widely considered to be a mistake that never should have been standardized in the first place, and Metal never supported them at all so they could only ever come up in old OpenGL code on macOS.
https://x.com/pointinpolygon/status/1270695113967181827