Why are some people in Argentina called Portenos?

"Porteños" comes from the word Puerto, which means Port in Spanish. Porteños was first introduced to describe the people that lived near the main Port in Argentina which is in Buenos Aires, the Capital of Argentina. So Porteños is used to refer to people that live in Buenos Aires. If referring to a female the right use of the word would be PorteñA, with an "a" at the end.