/ is used both in writing and in Maths. \ is a character used almost exclusively in programming.
From a practical point of view, I find \ to be a much more suitable directory separator than /, for the same reason I think Microsoft's choice for blacklisting characters like ? and : from file names is silly. There are real world use cases [1] for adding the / to file names so it shouldn't be excluded!
Microsoft has used the / for command switches since its inception, based on the way the DECS TOPS-10 (1970) used linker flags; with / already taken, they chose the Next Best Thing which is perfectly fine. When Unix came around a year after the TOPS-10 they used a forward slash for directories for some reason but there's no way one is better than the other.
For what it's worth, Windows accepts forward slashes. Since Windows 1.0, actually, all the way back in 1985. Try it for yourself in your browser[2], open notepad.exe and save a file in A:/test.txt. Your path separator may be represented differently, but / works perfectly fine.
Fun fact: in some locales (Japanese, for example) your path separator isn't even a backslash; the path separator is actually rendered as 0x5c, which corresponds to the Yen symbol in Japanese locales of Windows. In Korean locales, it'll show up as the Won symbol and you'll probably find many other path separator characters in other locales that existed way back in the console code page days.
Which is because not only Windows, but DOS itself supported it at least as far back as DOS 2.0 when they added sub-directory support.
There was even an option (in CONFIG.SYS) to alter the 'switch character', which then also caused a lot of command line tools to accept '/' for paths. That option was eventually removed from the config file, but the underlying API retained until quite late. Maybe it was WinME's version of DOS which disabled the API.
Despite all of that, the handle based Int 21 file APIs always supported being passed '/' as a path separator, and it was often accepted by some apps.
DOS based 'C' source code often used "#include <some\\path\\file.h>", however many compilers also simply accepted "#include <some/path/file.h>", probably just as an artifact of the obvious implementation. This wasn't well known, so lots of DOS based 'C' source used '\\' in includes, plus also at the file API level.
From a practical point of view, I find \ to be a much more suitable directory separator than /, for the same reason I think Microsoft's choice for blacklisting characters like ? and : from file names is silly. There are real world use cases [1] for adding the / to file names so it shouldn't be excluded!
Microsoft has used the / for command switches since its inception, based on the way the DECS TOPS-10 (1970) used linker flags; with / already taken, they chose the Next Best Thing which is perfectly fine. When Unix came around a year after the TOPS-10 they used a forward slash for directories for some reason but there's no way one is better than the other.
For what it's worth, Windows accepts forward slashes. Since Windows 1.0, actually, all the way back in 1985. Try it for yourself in your browser[2], open notepad.exe and save a file in A:/test.txt. Your path separator may be represented differently, but / works perfectly fine.
Fun fact: in some locales (Japanese, for example) your path separator isn't even a backslash; the path separator is actually rendered as 0x5c, which corresponds to the Yen symbol in Japanese locales of Windows. In Korean locales, it'll show up as the Won symbol and you'll probably find many other path separator characters in other locales that existed way back in the console code page days.
[1]: https://answers.microsoft.com/en-us/windows/forum/all/forwar...
[2]: https://www.pcjs.org/software/pcx86/sys/windows/1.01/