A 2009 paper from Institute for Creation Research claims that the reason no DNA has been successfully extracted from dinosaur remains is because any results that don't fit the evolutionary model are suppressed:

Because evolutionary scientists are committed to only publish dinosaur DNA data that match their naturalistic tale of origins. Despite the amazing discoveries of soft tissue from dinosaur bones, dinosaur DNA research results (and other dinosaur "connective tissue" research) continue to be steered by evolutionary dogmatism.