I just think that the writers really didn't want a job anymore.

Seriously though. I mean, think about the third season story lines. Khivar comes to the planet, but for two episodes and then disappears. I think Rath and Lonnie dropped off the face of the planet while Nicholas decided he wanted to be the poser child for Nike. I mean, all of their loose ends were left loose.
All of the destiny stuff was for nothing. Because, in the end, they just run away and live their lives like that anyway. Liz became a jellyfish, Maria turned into a child, and Max looked into a mirror and said, hey! I look good.
If you seriously watch season one and then watch season three, they were BEGGING for the show to be cancelled. Seriously.