Ni no did 1.4m worldwide DS+PS3. The DS version did 600k in Japan, which leaves the PS3 total at 800k; the game did around 200k in Japan, which leaves 600k units in Western markets. I wonder whether they could have increased the total volume of sales by releasing the DS version abroad, given how jRPGs performed over here on the platform.
Because Virtue's Last Reward sold less than 999 despite being on two platform and having a much higher budget (fully voiced, detailled 3d models, some 3d cutscenes, cost of developing on two different platforms...) than 999.
NDS Zero Escape: Nine Hours, Nine Persons, Nine Doors 16,967 / 44,367
3DS Zero Escape: Virtue's Last Reward 7,890 / 17,913
PSV Zero Escape: Virtue's Last Reward 6,133 / 15,454
They tried to expand the audience of the series by giving it bigger production values and it failed basically, sales would've probably been pretty similar had they stayed with a simple presentation like 999, and we would've gotten ZE3 years ago already.