Rust isn't designed to be "a better C++". It's designed to provide features C++ doesn't have:
-- Type/memory safety guarantees
-- Parallel programming with a guarantee of no data races (primarily by enforcing "no mutable shared memory")
-- Lightweight isolated tasks as a unit of failure
Developers who don't want those things should stick to C++. Developers who want all those things can't get them from C++ and should consider Rust, among other alternatives. Developers who want those things in a language which is as close as possible to C++ in performance should strongly consider Rust.