I'm curious, why not use LLVM?
Second aspect is I don't like the behavior of LLVM ecosystem which is trying to subtly EEE gcc toolchain.
Lastly, I don't desire to be able to build a project I developed, or cloned to be only can be built with "clang/llvm/20201024+somecompanyClosedGitBuild20210514+bp1" which is available in binary form for a single distribution for a specific architecture. I have experienced SDKs and other software like that, and I don't want to go through again, or put anyone through that hoops.
As opposed to GCC, which not-very-subtlety added extensions onto C which hurt portability?
GCC really shot themselves in the foot by making their architecture so difficult to use as a library, even from GPL code.