“What makes naturalization unnecessary?”
Ummm...naturalization is what makes a non-citizen a citizen. If they are born a citizen, then there is no need. And with a few rare exceptions, if you are born in the USA, or born to two US citizens while overseas, you are born a citizen of the USA - a ‘natural born citizen’, per the understanding of the folks who wrote and ratified the Constitution.
A statutory citizen (child born overseas with US citizen parent(s)) does not have to renounce the country of their birth before a Certificate of Citizenship is issued. A naturalized citizen must first renounce their citizenship of their home country before they are issued a Certificate of Naturalization.
The State Department has issued guidance it is the policy of the US to consider a statutory citizen to be a citizen at birth. Its debatable a statutory citizen, a citizen with dual citizenship after the Certificate of Citizenship is issued, it a Natural born citizen because of divided loyalty.
John McCain never renounced his Panamanian citizenship.