Earlier quoted context omitted.
Because people aren't robots. That's not how the brain works. People can't concentrate 100% for 8-12 hours a day every day consistently. >What if your supervisor could identify every time you paused to scratch or fidget, and for how long you took a bathroom break? I certainly wouldn't want to work under those conditions.
I get that this might be different in the US, but in Europe, there usually are minimum requirements for break time to ensure that workers aren't overly strained. E.g. screen workers should take regular short breaks to rest their eyes. In that case, tracking could actually be beneficial by making sure that nobody sacrifices their break time to improve their quotas. It doesn't have to be used for detrimental purposes (…
Beyond that, at least in office work, you'll regularly see folks eating lunch at their desk and working through it even though by law they're supposed to be 'relieved of all duties'. This isn't because some supervisor said so but because they feel obligated to do so.