Stop being lazy, go back to engineering first principles and it makes little sense to stay with C. [Insert systems programming language du jour] or any other well-developed language makes more sense.
It's the need to maintain super legacy systems and interoperability. There are entire CPU architectures that LLVM does not support and are only commonly supported by C and these things are still everywhere and are really gnarly problems to replace them.
Even if you throw everything away on the software side and start over from scratch, that's going to _force_ you to replace some hardware somewhere that you won't or can't replace.