Most people only cared about C, because they needed to work on UNIX, and UNIX was taking over the server room and all 1980's graphical workstations.

C was pretty much ignored on 8 bit home computers, outside some toy compilers for CP/M.

In the 16 bit days, it was yet another language alongside BASIC compilers, Pascal, Modula-2, Assembly.

C is so tied to UNIX, that POSIX had to be created so that any non-UNIX operating system could provide a cozy home for their C compilers.

UNIX/POSIX is for all practical purposes the runtime most C applications rely on, there are naturally some exceptions like free-standing or Windows (which eventually gave up and add to start improving its support).

It is only due to historical accident that Microsoft gave up on Xenix, instead of replacing their MS-DOS efforts.