With Rust, depending on what you're working on, you may lose almost no time integrating C and C++ (with an extern C interface) libraries, or you may lose 50% of it. Sure, you don't have to know CMake at least (which is a hard requirement for C++ nowadays), but using any extraordinary library dependency in Rust may prove to be a nightmare. Essentially: if someone else didn't already package it, prepare to lose some serious time. The language is nice, but the ecosystem is immature.
Things are probably going to change, and Rust will become more viable over time, but C++ is also improving at a rapid pace so I guess Rust will never completely outcompete it.