lthough the creators of the show had 
planned an ending to the show, the success of 
Avatar: The Last Airbender caused Nickelodeon to ask for more episodes.
[3]  The creators then came up with an idea of the next Avatar, this time a  girl named Korra. They decided upon a female Avatar after the large  audience of females of the original show and the adoration of the  headstrong female characters by the female fan base, and felt it was  time to have a big action franchise with a female in the lead instead of  the traditional male role.
[3]