BJ Penn was gassed and tired at that point. The first two rounds, Penn picked Fitch up, tossed him on the ground, got his back and went for a choke, and Penn could make 145, where as Fitch is a huge man at 170.
I don't think Fitch is being lazy, however, I think that he doesn't have the skill set to finish people. He's really the opposite of GSP, where as GSP does have the skill to finish people yet chooses not to, Fitch actaully tires but simply doesn't have the skill to do it. I respect Fitch for this, but he is still not an entertaining fighter.