> Since the forward slash was already used for CLI parameters in the CP/M style,...

> Since the forward slash was already used for CLI parameters in the CP/M style, it couldn’t be used as the path separator. So Microsoft chose the backslash instead, and it persists in Windows today.

It's a bit more nuanced than that: https://www.os2museum.com/wp/why-does-windows-really-use-bac...

And see also https://learn.microsoft.com/it-it/archive/blogs/larryosterma... for the SWITCHAR option, which would configure DOS 2.0 to use "-" as a parameter and "/" as a path separator.