New development in C++ would be a dire mistake, but you can't expect everyone to switchover on a moment's notice.
C and C++ are a liability for many reasons since memory corruption is notoriously hard to detect, localize and fix. And multi-threading is even harder, almost a dark science to get right.
The big one for me is that Rust packages tend to pull in dozens or hundreds of transitive dependencies - C/C++ code tends to be monolithic, so it has fewer maintainers who could become compromised.
