Never worked with VAX/VMS, however have spent enough time reading through its manuals.
Systems programming with compiled BASIC, its Extended Pascal version, the API surface that somehow we can find traces where Windows NT got its design inspiration from, really leaves some space for what ifs, in the operating systems adoption evolution.
The VMS influence is also why DOS and NT used / for options rather than - like Unix. I was a big fan of the CLD method of defining commands. It provided a nice standardized way of parsing command line arguments that was going to be consistent between all applications.
DOS uses / because programs written for CP/M, and which were subsequently ported to MS-DOS, used forward slashes.
when PC/MS-DOS 2.0 was released, with support for directories, it supported both forward and backward slashes for directory separator because Microsoft programmers wanted to use forward slashes (bringing them over from Xenix, including adding virtual "DEV" directory with device files), but for compatibility and user friendliness the default was \ for directories and / for options
Oops, the influence was a bit higher up the ancestry chain on both sides. CP/M uses / under the influence of VMS’s ancestor, TOPS-10. That’s what I get on relying on old memories of things I was told that were probably inaccurate from the start.