When you're paying someone to come into an office for 8 hours a day, you're paying for 8 hours of availability for work. Most of the time office workers don't have 8 hours worth of work, sometimes you have 2, sometimes you have 6, and sometimes you do have 8 hours worth of work.
In a typical office setting, in the time a worker doesn't actively have work they just pretend to be busy or sit around. In a work-from-home setting a worker can take that time to grab a snack, watch a video, spend time with their family, or any other number of smaller things.
While the freedom probably has been abused by people, this expectation of a solid 8 hour work day is being shattered and is showing how much more time and freedom workers can have compared to what we have right now and these CEOs are trying to turn it into a way to justify paying workers less or punishing them making use of that freedom.