So far there isn't that much stuff written in Rust, so, any non-trivial Rust program will link with a bunch of non-Rust code. On the project I worked on, we had to link with SPDK for example (a rather big iSCSI server implementation).

C++ has been around for... what?.. 40 odd years? And any non-trivial project still links with C libraries.

I don't see this problem somehow going away in Rust w/o some revolutionary changes in operating systems, which is the major supplier of decrepit but unavoidable libraries you have to link with in order to get anything done.