LLVM developers are focused on the needs of (literally!) millions of C and C++ programmers. Until you can point to a few hundred-thousand production Rust coders, or get somebody with deep pockets to depend on it, Rust is just not important enough. The solution is to fund your own LLVM developers. If you can't raise the money to pay them, who should?
People with deep pockets are typically advised not to depend on unsupported infrastructure. It is hard and, often, unwise to argue with such advice.
It is still early days. Give it ten years: Rust will either have taken off or sunk, by then. Maybe somewhere in those years there will be some new hotness to jump on instead.
The Rust of ten years ago bears almost no resemblance to the Rust of today. Its history is interesting to people involved in the project, but it wasn't really used seriously until 1.0 was released.
I make it 9 years since the first release and 4 years since the first stable version (aka 1.0).
Either way it's a short time in which to gain acceptance anywhere near the level of C++ so it's not surprising it hasn't. Although companies (including Microsoft and some Google teams) are just starting to take it seriously.
C with classes, which would be comparable to pre 1.0 rust, started in 1979, so 40 years ago. The first commercial C++ and the book were in 1985 and 34 years ago. I'd guess that's a good 1.0 milestone, comparable with rust's 4 years.
"C18 is a “bugfix release” of the C standard. Whereas the intention of the C working group (WG14) has been that this release does not introduce normative changes (but one)..."
People with deep pockets are typically advised not to depend on unsupported infrastructure. It is hard and, often, unwise to argue with such advice.
It is still early days. Give it ten years: Rust will either have taken off or sunk, by then. Maybe somewhere in those years there will be some new hotness to jump on instead.