^ I can't answer that but the article says the idea come from Sumo wrestling.
I don't know much about Sumo wrestling, maybe someone can help out. From wikipedia:
"kenshō-kin (懸賞金) Prize money based on sponsorship of the bout, awarded to the winner upon the gyōji's gunbai. The banners of the sponsors are paraded around the dohyō prior to the bout, and their names are announced. Half the sponsorship fees go to the Japan Sumo Association, and half to the winner."
EDIT: Actually when the candidates enter the stage for the first time during the conference the banner for each of their sponsors are moved across the stage.