It has. 80 years ago your worked more hours, and you could not slack at work. Today, you work not only less, but half of the people in the offices I go to don't work their full shift. They go to facebook, send text messages, take long breaks, do their shopping and watch porno (yep), etc. Also, an hour of work doesn't have the same value. When your work is moving boxes, an hour is an hour. But in an office work, there…
If there is so much useless/wasted time at office jobs, what's the practical purpose of requiring them to be there for a fixed number of hours?
First, employee don't want less money and fake it. Employers want the employee to be on site because they paid for it.
Second, society praises people for working. You will look better if say you are busy.
Third, our systems would collapse if people were actually paid to their real value. You would see the total unfairness of it, and also how truly brilliant or useless people are.
Fourth, laws, syndicates, medias and logistics come in the way. And with a big inertia.
Fifth, humans are not rational and don't do "the right thing" according to the intellectual or displayed objectives. And they have all their own agenda.