Why do we use "what" instead of "who" in "what is your name?
"Who" refers to people. "Who is your wife", "Who is your boss?", "Who is the local mayor?", "Who took out the rubbish" are all examples of "who", because they are asking for the person. But a name is not a person, it is an identifier of a person. "What is your name?", "What is your address?", "What is your car's number plate?" are all identifiers, not people.
So, you use WHO when you want to find out which person, otherwise, you use WHAT. The Name of a person is not the person, it is one of several identifiers associated with the person.