Because string processing is not slow enough? Making string operations eat the performance impact of that context switch in and out of kernel is not a good idea

Because string processing is not slow enough? Making string operations eat the performance impact of that context switch in and out of kernel is not a good idea. Library is better. This is not string but I'm thinking to some language like Rust where the "time" crate is not language feature but just about standard and all the other library use it. This is possible if a library like it is good quality and exist early in the language.