Is Yokohama a bigger stadium?
Don't know
Could be the answer, sort of, although in the case of Brazil the capital is a political capital hundreds of miles away from real population centres. Brasilia would never be chosen for any sporting final.2014 World Cup final was held in Rio because the stadium and infrastructure was better.
Yokohama is half an hour from Tokyo, according to Google, so just down the road really. Saying that, maybe the stadium and surroundings are easier to get in and out of, hotels more available etc. I know very little about Japan so I was just intrigued.