Because what I saw of him out of the court room told me he was a decent guy. Also he did his job well. If I ever needed a defense attorney, I would hope for one like him.
By that standard, Hitler could be praised for "doing his job well." Surely you don't mean this standard to be taken literally. And assuming you don't mean it to be taken literally, then you owe us a further explanation.
As for Cochran's decent behavior outside of the courtroom or his legal practice -- doesn't matter much to me. This man was a significant part of the ongoing corruption of American law and justice. And he conducted himself abominably in the OJ case. That's what matters.