EXO's popular there, but they didnt get more popular because of bad management. They debuted with a re-recorded single more than 3 years after their debut, them they release another single in 2016 and then, 2 years later they released their first album, 6 years into their career and it was when they were releasing their album that they made their first tv appearence on Japan.
Avex never spoiled their japanese fans, they only milked them making EXO touring there. That's what Japan was for SM/Avex: only a place they used to go to tour.
But they had such a big potential to hit big there. Growl became popular on Japan in 2013 and they sold more than 150k with XOXO, a non-japanese album. Still, they only debuted there 2 years later.
I could write a WHOLE BOOK about how EXO was mistrated and a waste of potential by their agency, cause I have so much to say