[Penny] may as well wear a sign from Joss reading 'Fall in love with this girl'. Except I didn't fall in love with her, because there's nothing to fall in love with. Joss didn't feel the need to give her a character, beyond 'sweet and unobjectionable', which are qualities I tend to look for in a cup of tea, not a likeable female lead.
It's always a bad sign when you realise that a character is so passive that they could be replaced with a carrot with no real difference to the story. Billy wants a carrot. Hammer has the carrot instead! Billy is emo and plans to kill Hammer to get the carrot. The carrot is killed instead! Now everybody is sad, as there is no carrot for anybody. The end.
Context picked up his motivation from the Anakin Skywalker School of Bizarre Reasoning. (QWP)