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".
Do you have any concrete examples for Python? As far as I know, ggplot2 is only for R. I would be interested to try out some alternatives to Matplotlib.
[1] https://github.com/JuliaRegistries/General
[2] https://pkgdocs.julialang.org/dev/protocol/