There are a few reasons why the 9th, 10th, 11th, etc seed don't get picked...
-The robot doesn't match the alliance strategy
-The team might have had a few lucky breaks being paired with great teams to push them higher.
-Not enough PR/visual appeal power (small teams suffer from this)
-Didn't play the game the right way (i.e. smaller pusher bots vs. cappers)
Remember, it's not a game until luck is added.
