My point is that reproducible builds in Go and Rust are much, much easier than C and C++ (and Python since everything depends on C and C++). If your C and C++ programs are building easily (including their direct and transitive dependencies), then you're almost certainly not doing truly reproducible builds (or perhaps you're just very, very familiar with your particular dependency tree in a way that doesn't generalize to arbitrary trees).

To be clear, I'm not arguing that there are better tools for working around C/C++'s build ecosystem; I'm arguing that our lives will be better when we minimize our dependencies on those ecosystems.