Maybe the characters' goals are constantly changing or being postponed. When characters don't have clear, consistent goals, the story can meander and seem never - ending.
One reason could be that the game doesn't have a very engaging story or characters. If a game lacks these elements, fans may not be inspired to write fanfic. For example, some simple puzzle games may not offer much in terms of story for fans to expand on.
It could be due to a variety of reasons. Maybe it's a genetic factor or a result of certain lifestyle choices like not getting enough sleep or poor diet.
Well, there are so many fanfics out there that it's easy for some to get lost in the shuffle. Also, with new shows and stories constantly coming out, people might move on from Naruto fanfics.
Routine is the main culprit. We often follow the same schedule day in and day out, like getting up at the same time, going to the same work or school, and coming back home in the same way.
Perhaps the setting and world-building are weak. A poorly constructed fictional world can make the story seem insubstantial and like it's missing a real backbone.