The Hot and the Dead

I wonder why threads go dead so quickly. Is there a minimum post requirement within a limited amount of time? Also, what determines a thread to be "hot"? Does a dead thread ever have a chance of resurrection, with a certain number of posts, to become a hot thread? Just wondering.:)

Hot is just given when a thread hits x number of replies or x number of views. There is no associated time limit.

I am curious though how the New Posts listings work. How come sometimes 50 might show up and other times three or four?