Very happy for this one. Because it could have just as well sold as 'little' as P3 and P4, which would have been fine. But I was always sure that more people would be into this series if they just gave it a chance.
I attribute much of this growth to the eye-catching presentation of the game.
I'd probably attribute a lot of it's growth to P4:Golden tbh. The vita release of Persona 4 really seemed to elevate the series in terms of how many people actually knew about it in the West. I'd never heard of Persona before it. Maybe that's just me.
But it somehow sold more on the Vita than the PS2 so I guess that shows that the franchise was definitely growing with that entry.