I don't have it in me to to work in front of a screen all day, although I understand that works for many on this site. I don't care if the workplace is an open office, a cashier's stool at a supermarket checkout, or a train driver's cab.
Although the common use would be funny here :)
We don't pay firemen to put out as many huge fires as possible all day long, because that would lead to very peculiar and unwanted behavior incentives to max out those metrics. Firemen hiring pyromaniacs to make them look good, etc.
Plenty of jobs out there where the metric you're trying to maximize is internal/external customer satisfaction, usually something like maximize service uptime. If your assigned responsibility is the accounting dept, and the accounting dept loves you because when they report a problem its rapidly fixed, then you're doing what the company needs.
Some companies refuse to metric stuff like implementing change, because it results in I (heart) change for the sake of change. I quickly close a ticket to tweak the background color on an internal app but that doesn't make the company any money.
There are jobs like mining coal or farm work, where paying you to not produce makes the owners very angry. Sometimes being in a non-productive cost-center has its privileges. "You're paying me so IT is never in the way of production dept" or IT never gets in the way of accounting so accounting never gets in the way of the production dept, etc.
Big industrial factories usually have a maint department whom do nothing but fix machines. If none of the machines are fixed you don't punish the maint dept LOL. Usually they have pointless busywork if nothing else is going on "go repaint the milling machine". Such things exist in IT "go update the reverse DNS records".
About 4 hours is peak productivity.
We don’t need you to work extra to satisfy our god complex.
When swe work conditions discussion reaches this point I always remember Spolsky's brilliant "Smart and Gets Things Done" book. He writes about KPIs a bit, just enough to not treating it too seriously.