I believe Julia only uses the Git registry as an authoritative ledger where new packages are registered [1]. My understanding is that as you mention, most clients don't access it, and instead use the "Pkg Protocol" [2] which does not use Git.
This is true for many functions, but afaik the llvm code is only generated for a function paired with the types of the arguments that it was called with. Since Julia functions are for the most part 'generic' and work with a wide range of argument types, you would have to restrict the compiled binary or library to a specific set of argument types. Some functions also have type instability and can't be made into pure llvm.
It seems you think their mistake was using C in the first place, and not the way they used C.
Calling people out for not using a language that you prefer is not helping them learn, nor is it bitter medicine to those who find learning your preferred language "hard".
[1] https://github.com/JuliaRegistries/General
[2] https://pkgdocs.julialang.org/dev/protocol/