It's very much easier to measure hours of physical presence than actual value of a worker's output. The other problem is that if you measured people purely by

It's very much easier to measure hours of physical presence than actual value of a worker's output. The other problem is that if you measured people purely by output, 10x developers (assuming you believe in such a concept) would be able to work 1/10th as much and would very visibly be missing much of the rest of the time. This would lead to a lot of resentment from people who are less productive and would be having it rubbed in their faces. To get to a place where people are judged purely on output we would need to change society such that the notion of equality was essentially never mentioned or thought about at all. Because people's productivity is wildly, wildly unequal.