Because which employer we work for is voluntary. If I own a business, I can choose which systems I implement in order to ensure a certain level of quality. If I had a logistics company, would it be inhumane to install cameras in the truck and GPS devices that monitor speed? Absolutely not. There's something called "risk" and from a business standpoint, it needs to be mitigated and controlled.
That is why, as employees, even certain key words are monitored on our computers. If we're in a relationship with a co-worker, it needs to get reported. The list goes on.
A critical part of fast food is customer service. If customer services goes down the drain, that presents a very real business risk to Burger King.
To a certain extent, this has been a standard practice in the field of customer service representatives that are taking calls all day. Their calls are monitored and recorded, then reviewed to ensure a certain level of performance.