Imagine how much impact we could have if we used all the effort gong to develop Rust and port everything over to Rust to instead just improve the wrinkles that exist in C++.
Most of the worst issues with C++ can't actually be fixed without backwards incompatible changes that would break large amounts of existing code. Google spent several years advocating for the approach that you're suggesting, but was unable to persuade other members of the C++ standards committee and recently announced that they're working on a replacement language. The rationale for Carbon goes into great detail on why fixing C++ isn't a viable option.
https://github.com/carbon-language/carbon-lang/blob/trunk/do...