Even in a modern Unix, globs are expanded by the shell before invoking exec(3) with the individual arguments split out. They are not split/expanded by the C runtime.

...and I'm pretty sure DOS inherited it from CP/M.

‘Implement’ isn’t necessary. That code could be provided by a shared library.

That could be the superior option. Moving command line expansion into a shared library gets rid of the problem where the command line with globs expanded is too long, could have standardized option handling earlier (that system-provided library for globbing could easily grow to handle option flags), could better handle file names containing spaces, etc.