A piece needs to be 10 days old or less.
Then it needs five different voters to give it a score.
Then it needs to have a high score.
But if there aren't enough pieces that satisfy criteria 1 and 2, the top ten shrinks to a top 9 or 8 or whatever.
when traffic is low, and the top ten shrinks, you usually get a "hated" piece (racist or has dead children in it) at the bottom of the top 7 (or whatever) because it pissed people off enough to make them give it one star.
Summary:
If it's #6 in a top six, then it's because it's unpopular.