>> I bet somewhere in there there's still UI that dates back to Win3.1.
I'm sure there is, that's a mix of backwards compatibility and don't mess with stuff that works. Some people want it, some people don't; can't make everybody happy. Can I complain that OS X provides a terminal that looks like it dates back to the 70's?
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].
[1]: https://blogs.msdn.microsoft.com/oldnewthing/20071231-00/?p=...
I just ran Win10 for the first time yesterday to work on a security guideline and I was blown away by how janky the whole thing was. Using it is like crawling through 20 years of computer history; there's things from every phase of Windows since '95 in that UI, and I don't mean UI hints, but entire applications.
I bet somewhere in there there's still UI that dates back to Win3.1.