Revealing mistake: When Nat enters Nick's loft from the lift, the bright lighting reveals that there is no break in the solid floor to allow the movement of a real elevator. (00:36:45)
Revealing mistake: When Robert is shot, the car blowing up in the alley is sort of half an explosion, abruptly curtailed. Severely cold weather during shooting literally froze the cameras and left only a few seconds of usable footage. That snippet is repeated for effect, but the explosion still looks "cut off" because it is. (00:32:00)
Revealing mistake: When LaCroix opens the box containing Divia's little "surprise," the severed head's eyes move slightly as the covering tissue paper is removed. (00:07:20)
Answer: Nick was sick and tired of being an immortal bloodsucker. He wanted to be human, fall in love, get married, have children, grow old and die. As for Janette, according to her, she fell in love and the passion she felt "cured" her of her blood lust.