Here is a short answer. The hard drive industry is the backbone of modern computing. A hard drive offers economical storage space. But with limitations. One is spied. It is very slow compared to the CPU and memory.
Another issue is reliability. The hard drive has to compensate for failures that happen. Whenever you format hard drive the internal firmware makes needed corrections to the drive map. This means that bad spots on the disc are masked and are no longer available to the system.
So when you formatted the hard drive, you 'fixed' it in manner of speaking.
Sorry, I do not have a reference. Years ago I worked in Silicon valley and I was in the Hard Drive research portion of a major company. Some work we did was with Stuttgart, who later founded Segregate. Even back then hard drives had a self healing feature. Whiteout that, they would have been useless.