This NY Times article explores why the number of decisions by the Supreme Court has decreased so drastically. My favorite explanation is that since the Court is so divided that the judges are scared of granting a petition for fear of not having the number of votes on the court to win the decision.
My second favorite was that the number is going down because law clerks make the initial recommendation on whether to grant cert., and the law clerks are afraid of looking stupid so they don't recommend as many cases. That's a gas. The greatest legal minds of our generation (or at least the ones who get good grades at good schools) are too timid to take a stand.