Look at what Shaq shot from the field as opposed to free throws. Many instances like this including with otherwise good shooters who simply sucked at free throws.
Well, part of that can be explained by him being over 7 feet and weighing 325 pounds; he was also pretty agile for his size. He was very tough to stop once he went into his move. That's why Detroit made the very wise decision in the 2004 championship to defend him primarily by denying him the ball.