Read the 14th Amendment to the Constitution again. Why do you suppose the put in the clause, "and subject to the jurisdiction" if the sentence would have meant the same thing without that clause?
That's a good question, and I don't know the answer, but will be anxious to find out the answer. However if you defined someone as "not subject to the jurisdiction of the United States" how would you deport them, or prosecute them for various crimes? Possibly it's to cover the children of diplomats. I'll bet it takes a bit of research to find the original intent of that clause.
I don't think it can be that Congress can just declare a class of people "not subject" and deny them citizenship, else some future Congress could have declared all blacks to be "not subject" (or all redheads or people of German ancestry, etc).
Nice try. I've said the same thing repeatedly, but most folks refuse to understand that the 'United States' in the Constitution does NOT mean the entire country......
No matter HOW many times the government says it does. :)