> Especially since Terminal.app is far more modern than CMD.EXE?
To be fair, a lot of Terminal.app dates back to ancient Mac OS too. The menu bars, for example, are all still Carbon. There is still a full classic Mac OS main loop running alongside the Cocoa main loop in every macOS application. Apple's done a good job hiding it, but it's still there.
Anyway, cmd.exe is a bit of a special case. What you're really seeing is conhost.exe, which is kept the way it is because it's part of CSRSS, which occupies a similar place as PID 1 does, and Microsoft doesn't want to bring new UI into it for fear of increasing its dependencies [1].
