You are misinformed. Dragon Quest sells under a million worldwide outside of Japan. Tales has only ever had 1 game break 1 million units sold worldwide. Shin Megami Tensei has never broke 1 million units sold worldwide. Even in Japan RPGs are by and large low budget and low sales productions. This was true last generation and it's true this generation as well. I know my RPG history hehe. I've played JRPGs practically relgiously since the SNES.
The JRPG market has been shrinking at an easily trackable rate since FFVII, and this generation could represent as much as a 50% drop in sales for the genre as a whole. JRPGs are niche, even in Japan, other than a few main series. Budget constraints are forcing the majority of new RPG development on the DS and Wii.
If that is true, why are JRPGs decreasing in popularity then?