That's because Broly is famously known as the Legendary Super Saiyan, at least in Dragon Ball Z. To this point, the DLC for Kakarot has covered the Battle of Gods and Resurrection 'F' movies ...
At the end of Dragon Ball Super: Broly, when Goku finally had a chance to formally introduce himself to Broly, he introduced himself as both Goku and Kakarot. Goku had always rejected his Saiyan ...