I think this issue is a bit overstated. What people want is not to have interop with existing C++ code, but to just keep writing C++ in the same idiomatic style. And this just isn't feasible if you want to automatically ensure memory safety. It's especially problematic in larger codebases that can't be comprehensively surveyed, which is what people mostly want to use C++ for. So, something has to give.

Rust is a bit of a different story, because the clunkiness of Pin<> actually makes interop with C++ (and, to a lesser extent, C) surprisingly difficult in a way that might be amenable to improvement.