Probably just divine intervention. The goddesses need a hero to use the Triforce of Courage and defeat evil. Who better than a reincarnation of the guy who defeated Demise?its never fully explained why link like zelda and demise(ganon) keep coming back
if the original chosen hero of the goddess is the first (non time traveling, or even the creator of the time portal in SS) "link" that would make it make sense.