There are other languages such as Ada that allow you to more precisely specify such things. Before requesting many new types for C, one should clarify why those languages did not already replace C.

I agree though that using "unsigned" for non-negative integers is problematic and that there should be a way to specify non-negative integers. I would be fine with an attribute.

The problem is also that the standard committee is not the ruling body of the C language. It is the place where people come together to negotiate some minimal requirements. If you want something, you need to first convince the compilers vendors to implement it as an extension.