The advantage of having multiple C compilers has always been broader platform support and competition to improve compiler speed, error messages, and codegen quality. Conspicuously, one complete non-advantage of having multiple C compilers is portability of a codebase between compilers; the C specification contains too much implementation-defined behavior (including undefined behavior) and is too anemic (requiring compilers to come up with nonstandard extensions to support things like assembly and SIMD) for compiler-portability to be anything other than a nightmare for large projects. C projects even have a hard time upgrading to new versions of the same compiler, which helps to explain why so many shops are still using positively ancient versions of GCC.