Why didn't Obama use a Bible the second time he took the oath?

I have read many reasons why this was done. Conspiracy theorist come with a lot of imagination these days. The first oath was done over the 1861 Bible President Lincoln used wich is not mandatory as only a tradition started by The first President George Washington. I believe an oath is like baptism. Once you baptise you dont need to baptise again, you just follow along with your faith the rest of your life. Obama took an oath over The Bible and one is just enough for the rest of his presidential mandate.