Indeed, we have our own bootstrapped Rust toolchain internally. I think this has to do with (legal) certifications, but I'm not entirely sure about that.
BTW, are you aware of the Bootstrappable Builds folks achievements? Starting with only an MBR worth of commented machine code, plus a ton of source code, they build up to a Linux distro.
https://bootstrappable.org/ https://lwn.net/Articles/983340/ https://github.com/fosslinux/live-bootstrap/blob/master/part... https://stagex.tools/