MapleStory 2, welcome.

Any reason for it not doing well?

A lot of the English community quit because of how casual the game is. Equipment/upgrade system is trash (seriously, they could have done so much better). Actual content is very slow. Little to no skill is involved in any boss fights - they are pretty much all DPS races. Damage comes solely from weapon enhancement, which is 110% luck.
There was basically no economy until rather recently, when they started allowing certain equipment to be traded.
Rumor is another class is already being planned.

I personally don't think we'll ever see a version for NA.