Yes, because C is, by virtue of its history and central role in the development of all mainstream operating systems, the lowest common denominator.
Also, if I remember correctly, the first Rust and Go compilers were written in C.
OCaml was used for rust.
> Yes, because C is, by virtue of its history
Sure history is great and all, but in C it's hard to say reliably define this int is 64-bit wide, because of the wobbly type system. Plus, the whole historical baggage of not having 128-bit wide ints. Or sane strings (not null terminated).
Yes! It's easy to see why we got here, but that doesn't mean it's the optimal outcome!