The president invited 12 drivers from the 2010 Chase to celebrate their successes. The drivers bailing include Greg Biffle, Tony Stewart, Kevin Harvick, and Carl Edwards. Jimmie Johnson, Denny Hamlin, Jeff Gordon, Kyle Busch, Kurt Busch (who had initially declined), Clint Bowyer, Jeff Burton and Matt Kenseth all are planning to attend.
While the absentees may indeed have scheduling conflicts, we'd expect that if that were the case, it'd hold true for the majority of those invited. Also, passing on the chance to meet the sitting U.S. president, regardless of one's views, seems like an odd move.