It has everything to do with the games. The 3ds's library is currently so much better than the psvita's its not even fair, especially in Japan. Not only does nintendo now have Monster Hunter, but it also has Pokemon, Animal Crossing, and New Super Mario Bros which are all bigger than monster hunter in Japan, and Mario Kart looks like it will become bigger than monster hunter as well.
The only psp games to sell over 1million copies in Japan were the Monster Hunter games. The DS had 37 different games sell over 1mil in Japan. Sony literally has next to nothing now that they lost their only big portable franchise in Japan. Heck next week the 3ds will pass the psp in number of games that sold over 1mil in Japan, and it's install base is less than half the psp's.
