If you've spent enough time at the lowest level of gigahertz clocked hardware you know that you'll never be able to even map a single second of a modern computers execution in a lifetime. You will always have to deal with simplification and approximation, which means you might miss a crucial detail.

Finding a bug is usually starting from a very high degree of knowledge about the designed function of the system and verifying at ever higher resolution that it actually performs according to those designed parameters. That's different from trying to understand what a computer does starting from an electron micrograph of the chips and not having access to the software or the wiring diagram. That might lead to useful insights but it wouldn't be understanding.