You right. Always good to remember that Apple was and still is the main company behind LLVM.

Swift was built and its maintained by the same time that worked in LLVM.

And also, Swift has its own fork of LLVM and LLVM has built-in a lot of features designed for swift like calling convention and async transformation.

The amount of features swift has and is releasing at the same time it has its own LLVM version is just not a thing you can do without a lot of money and years of accumulated expertise.