Why did this horrible language become so popular? I wouldn't call m4 "popular" in the slightest, it's generally used by only a few well-known programs like aut

Why did this horrible language become so popular? I wouldn't call m4 "popular" in the slightest, it's generally used by only a few well-known programs like autoconf, sendmail and SELinux. It's used because it's a standardized way to bolt on substitution macros to a system without having it be intrinsically aware of them.