Here are the options for Japanese third parties right now
1. 3DS - Leading plat form, but it is weaker and competition is stiff with major IPs (Monster Hunter, Pokemon, etc.)
2. PSV - Secondary plat form, stronger and easier to do cross platform titles on PS3 or even PS4
3. PS4 - Despite success in the west slow to transition to new system, 2015 and 2016 will likely see the shift happen
4. Wii U - Poor sales world wide make the system not that appealing
5. X1 - Dead in Japan and demographic of western owners don't help either
Of course...then there are phones which is the real #1 in Japan.
So, when you look from their view the Vita isn't a big risk and many companies have found success on it. Especially given Sony offers little competition in software so it essentially is a third party system.
