It was born in an era when there were many different *nix versions, all slightly different, with different names for include files, different C compilers with d

It was born in an era when there were many different *nix versions, all slightly different, with different names for include files, different C compilers with different flags, etc. Different OSes took differing numbers of arguments to certain library functions, etc. It was a necessary evil in the 90s. I still remember the perl config script that would say "Congratulations. You aren't running Eunice!" (Eunice was a bsd unix compat layer for VMS)