Reasoning for Japan hosting, easy to get to (relatively), lots of cities with appropriate sized arenas (some are dated but in the size), good transportation system between cities, good hotels in those cities. Willing TV stations (Fuji and TBS) and sponsor money.
TBS has the rights to the World Championships when Japan hosts them (and even overseas in 2014), so no vabo-chan, but Volleyboo. Where as Fuji had both the World Cup and Grand Champions Cup.
Fuji is invested in the Haruko national high school tournament, so it make sense for them to promote national team after they are high school stars. Fuji also now has invested in a new volleyball anime project "2.43".