^Or its the fact that Japan's market is already flooded with that genre of film, but the Japanese have done it a lot longer and better with deeper storylines on televised mediums. Besides it could be that there's market hesitation over the fact that the DBZ hollywood adaptation fell flat and were trying to avoid American adaptations.
It's probably a combination of said market saturation, and big-dumb fatigue. After so many pretty but vapid action films, here comes another one. And even though Pacific Rim has more going for it in tone and execution, it's still perceived as yet more big-dumb.
Regarding adaptations, it's probably not this, since Pacific Rim is just a genre film, and not a choppy adaptation like that DBZ film.