Because even the most careful C++ programmer still makes plenty of mistakes. Not the, "oops I cut my finger," kind. Those are usually found by linters and analy

Because even the most careful C++ programmer still makes plenty of mistakes. Not the, "oops I cut my finger," kind. Those are usually found by linters and analyzers. More like, "there's a PCI breach and now we're liable for millions of dollars," kind: the semantics of C++ are hard to nail down and ensuring that private data doesn't leak to other threads is almost impossible to get right with only knowing C++ and being careful. You generally need to use higher-level tools for that kind of work: Coq + the Iris framework, for example, in order to prove that your system can freely share memory and not leak secrets so long as X, Y, and Z hold, etc. Or you need to run a ton of tools like Jepsen to find if your system behaves the way you think it does. What baking more of the specification language into the programming language does (ie: better type systems) is enable us to have more of these guarantees earlier in the development process when changes are cheaper and faster to make (at the expense of requiring more expertise to use them).