Figures from Atlus' parent company in Japan suggest that 260,000 Japanese gamers have picked up Persona 4 Golden for the PS Vita, and with just over 1,000,000 consoles sold over there, that means it has a rather neat attach rate of 1-in-4. Hatsune Miku isn't far behind on 200,000+ sales.
If only a few more Vita games had that kind of magnetism, the console might be selling a bit better. You also wonder why Atlus US has spent so long in getting over to the American and Europe. How many Vita owners will have given up by the time the game finally arrives?
While comparisons aren't really appropriate, the likes of the original Halo had a 33% attach rate and Mario games are probably 50%+. Sony will be sorely disappointed by the sales of all of its big franchise games with only Uncharted selling any big numbers (around 750,000 worldwide, and still being promoted in the latest Vita adverts). The next highest Vita game is Gravity Daze with around 1-in-8, but that excludes digital sales.