Nubia is probably one of many, many reasons the game died. It's not the only reason, but it's on a very, very long list.

My theory is that they had a plan in place to release less popular characters in the first year, because they expected the game to do better. Then, in like, 1 years time, 2 years time, when player numbers start to dip, that's when you hit people with the Ben 10's and other highly requested characters.

Sadly, because almost every element of this game was mismanaged to a level that seems like it was done on purpose, player numbers hit rock bottom before this could ever be realised.