I think most C++ developers do see the value of something like Cargo…but it must also be considered that making it easy to bring in dependencies does not also mean the standard library can be poor and you can farm everything out to third parties.

C++ does not have a standard checked arithmetic operation, so I'll concede with you there. It really should, although most people just use the fairly widespread compiler builtins that behave similarly. (That being said, having it not be the default means that people who really need it won't use it, which is the same situation that Rust is in.)