There's a multitude of reasons why you might miss out on a Kickstarter campaign. But just because the timer's run out doesn't mean that you have to miss out. Case in point: Renegade Game Studios is currently taking late pledgs for their Terror Below game.
From the announcement:
Put on your boots! It's time to wrangle some worms! If you missed out on backing the Kickstarter, you can still get your hands on the game with the Kickstarter exclusive Hidden Cache with a late pledge - but you better act soon because it'll only be open for a limited time.