Another factor is politics:

A friend of mine was convicted of insider trading. He was CEO of a big company whose stock tanked during a general meltdown of that industry's securities about 10 years ago. A three-judge appellate court ordered a new trial. But then the prosecutor asked for another hearing en banc. That court voted 5-4 to reinstate his conviction. One of the judges who voted against him was assigned to hear his appeal to reduce his sentence. She didn't have to recuse herself. Up for re-election in a state in which everyone hated my friend, she didn't reduce her sentence.