Over the past 20 years GCC and GNU/Linux have gone from negligible to overwhelming market share in the fields of C compilers and POSIX-on-the-server, thanks in large part to the massive software ecosystem that has developed which can only be compiled using GCC and its non-standard language extensions, and/or can only run on GNU/Linux and its non-standard extensions to POSIX.
Once enormously-popular competing implementations, Borland C, Solaris, etc, have been "extinguished." Surviving and new implementations treat GCC and GNU/Linux as the reference standards more than anything the ISO puts out.
Again, I'm not saying that's a bad thing; just the opposite. Inferior products (which can and do include the published standards themselves) were beaten out by superior ones.