Herb Sutter briefly talked about why carbon was not a good contender, and I think remembering it was because of backward compatibility with C++.
At some point, keeping C++ semantics matters, since having different semantics would obviously prevent using previous C++ codebases, or make it more difficult to make those work together, and that may be why Carbon may not be a good choice.
At some point, keeping C++ semantics matters, since having different semantics would obviously prevent using previous C++ codebases, or make it more difficult to make those work together, and that may be why Carbon may not be a good choice.