Why isn't the Vita selling in massive quantities in Japan? Because the PSP is still getting all the best games would be a fair answer (and Japanese gamers are smelling blood and waiting for that dripping price cut). Again, a PSP title sits on top of the charts, this time - Super Robot Wars Z 2, which sold over a quarter of a million UMDs to happy portable gamers.
With three other PSP titles in the top 20, the venerable system is doing great and Sony is now probably suffering a backlash from the huge PSP sales that it was enjoying well into late 2011. There's more to come too with a new Akiba's Trip and plenty of other games recently announced for PSP. While Sony is still selling loads of PSPs too, it probably won't feel the need to cut the Vita's price, but every week lets the 3DS race further and further ahead.
The top three looks like this:
[PSP] 2nd Super Robot Wars Z Saisei Volume (Namco Bandai, 04/05/12) – 265,439 (New)
[3DS] Kingdom Hearts 3D: Dream Drop Distance (Square Enix, 03/29/12) – 42,231 (255,810)
[PSP] Pro Baseball Spirits 2012 (Konami, 03/29/12) – 26,908 (87,049)
And the hardware charts show the Vita suffering a sizeable drop below the 10K mark:
3DS – 72,115 (121,921)
PlayStation 3 – 19,370 (23,771)
PSP – 14,804 (18,356)
PlayStation Vita – 8,931 (12,105)
Wii – 7,099 (9,292)