1. He impeded efforts to assess the damage he inflicted. He refused to state what documents he took; he also lied outright when asked what documents he ordered on behalf of Israel.
2. He expressed no remorse for his actions.
Bottom line: Pollard didn't "mishandle" classified material. He willfully delivered it to a foreign power, then refused to help clean up the mess.
Pollard's sentence was enhanced because he was an American Jew who spied for Israel. There is a deep and abiding visceral hatred for him that is not present for other spies.