Why do all of the Maple copy cat games keep dying?

Sure, we know that Maplestory is one of the better 2D rpgs around but how come it has so little legitimate competition? Is it really that hard to not blatantly copy someone elses work and create something original? And how come there are not any 2D MMORPG developers in North America?

Come on guys, we need some more games like Maple but that are not cheap knock offs!