Hard drives were not designed to endure massive impacts while running. This is common knowledge now, especially with the advent of portable external hard drives that can easily tumble off a user’s desk. When our data recovery engineers perform dropped external drive data recovery operations, there is a wide range of specific drive failures they see.
When a hard drive takes a dive while running, the read/write heads are the most common casualty. Sometimes, the platters themselves are spared damage, especially if the drive has an accelerometer inside it that can detect when a drive enters free fall. Some hard drives actually work just fine for a little while after taking a tumble, until they eventually fail. But another hard drive that falls from the same height might experience catastrophic failure.
One human, after all, might survive falling from a great height, while another might die falling from the same height. Falling off a three-story building onto your head will probably kill you, while falling off a three-story building and landing on your feet would more likely break your legs and shatter your ankles. (You won’t be walking away from either fall, but you may be able to crawl away from the latter.)
Hard drives are mostly the same. The problem is that hard drives are very sensitive, and they cannot shrug off or recover from injuries the way we humans can. You just can’t get data off of a hard drive that isn’t in peak (or reasonably near-peak) physical condition—that is, unless you’re a data recovery expert.