Why is it that only western comics make successful movies, while eastern ones like Manga don't?

I noticed through out the 90s all the way up into today, comic/graphic novel adapted movies from the Western hemisphere- from the US (mostly) or Great Britain usually become big hits or cult clics while ones from Japan never get wide release spreads or get critically panned if they're live action (ex: the Guyver, Dragon Ball Evolution). I mean if you look what's been playing- Thor, Green Lantern, Xmen, they become Block Buster hits. Japan's 2nd most successful anime "Howl's Moving Castle" isn't even based off a Manga, its a British Graphic Novel. So what I'm getting at is are comics and Graphic Novels better than Manga? It seems so because of all the movies and high sales of comics. Even if the movie doesn't become a Block Buster Hit, it eventually becomes a cult clic- EX: The Punisher, or even the crappy Scott Pilgrim Vs the World.