I think the argument is that most people are truly only attaining maximum productivity for 5-6 hours in a day, so why are they even there for the extra 2-3? If you make $100/hr for 8 hours but are only productive for 5 of those hours, your employer is really paying you $160/hr. Why are we wasting employees time and employers money?
This is very IT-centric point of view, where mostly creative work can be done in various speeds, depending on effectivity and motivation in given time. I know its definitely valid for me and colleagues.
Imagine tons of other jobs where this simply doesn't apply - doctors, teachers, bureaucrats, farmers, drivers, shop/restaurant crew, people working in tourism, many factory jobs and probably tons of other types of jobs. Yes, I just mentioned more than 90% of the world population.
We can gradually improve efficiency of probably every single job out there, but simply slashing 30% will have very direct negative consequences on output for most people, in many cases directly proportional. Now who wants to take 30% pay cut?
