hmm.. I guess hana yori dango played big role , the fact that they have got lots of acting roles good actors , their singles albums .. they're CMS .. they never rest
they're nice in person .. they're friends more than a band
it's like you're watching friends who started together not a normal boyband
they're bond with eachother might be the reason ne ..

Yamada Tarou also ?
them playing live actions might drag manga/anime lovers too
their different personalities &hearts
they are good comedians too! and their concerts , their AAA concerts <3

that's all I could came up with at the moment !
good luck betty !! &hearts