The fanbase was there. There were definetely several modding groups and projects at the time, but they eventually withered. Online play was also strong for a brief period, then also waned. Much like Neverwinter Nights the main portion of the game was passable but players tried to extend its longevity by using the toolset and playing online.
The lack of a meaningful fanbase was not exclusively due to the main game's low points. Sure, generic and uninspired gameplay helped, but so did the game's attempt to be a varied package, and it having better competition (not necessarily genrewise).