If anything this argument would make more sense the other way around: Rust cares about memory safety a whole lot more than C++, so it should be more concerned about having insecure interfaces leaking through dependencies.

C and C++ don't have bespoke build and module systems because it wasn't really a thing back when they were conceived, that's it. And bolting that stuff as an afterthought on top of existing, widely popular languages is extremely difficult.