I think the franchise got off to an ideal start with Dragon Warrior 1 on the NES (overproduced and given away for free = great advertising), but it couldn't match the Japanese success because you can't always replicate a phenomenon. The game just didn't resonate with large numbers of American kids the same way it did with Japanese kids. But it did resonate with some American kids, and (after Dragon Warrior 1) it was the NES RPG series, and sold better than most NES RPGs.
Then Enix (in America) stumbled and missed the boat on the RPG superconsole which was the SNES, because their expectations were set too high, and if they weren't a phenomenon, they didn't care.
Dragon Quest missed it's chance to become Final Fantasy 7, but that was never going to happen because Final Fantasy was trying to push the boundaries of flashy presentation while Dragon Quest tried to step away from flashiness. They tried to ride in on FF7's coattails and sold better than most PSX RPGs (despite their strategic blunders), but that still wasn't good enough for them.
They put a massive effort into DQ8 on the PS2, and they sold better than most PS2 RPGs, but again, anything less than a phenomenon is seen as a failure for Dragon Quest.
The DS games sold great. Fail. Not even worth bringing them over.
This is not a series that ever puts in the work required to build a brand (although they're plenty happy to sabotage it repeatedly), and it wins in spite of itself (why else do we even have threads concerned for the series?), but those wins will never be enough in a world where Dragon Quest became a phenomenon on the other side of the ocean, and Final Fantasy and Pokemon became phenomenons over here, so people ask "Why can't Dragon Quest be a phenomenon in America too?"
I don't buy that a few people being turned off by Akira Toriyama's art is a real factor, seeing as how Chrono Trigger is widely regarded as one of the greatest RPGs of all time, and DBZ is as mainstream as anime gets in America. And I refuse to believe that Tetsuo Nomura's belts and zippers are the key to success over failures like Akira Toriyama and Yoshitaka Amano. Is the only acceptable-by-Americans alternative to Nomura's belts and zippers Motomu Toriyama's waifu Lightning? Because if it is, I don't know if I want to live on this planet anymore.