This isn't so much a cmd thing as a fundamental Windows API thing. CreateProcess takes in the entire command line as a single string.

Powershell is a completely different model where native commands run in-process, you can import commands and invoke APIs from arbitrary .NET assemblies, and then the PS runtime handles all argument parsing (and many other things). But it also lets you invoke and interop with arbitrary command-line executables and then those do their own parsing like they always have.