I think the idea is that a 4-day workweek would come along with a broader cultural shift.

Imagine a world where Saturday was a workday, it shouldn't be hard as this was the case for many only a few generations ago.

We could say that it is expected that you will not only work 48hrs/6 days a week, but probably 70, 80, 90 hours likely 7 days a week!

Fortunately, a cultural shift occurred along the way, and the work week is now commonly accepted to be 5 days. Expectations of clients, managers, and employees are based around this standard.

So why can't the standard change again? Why couldn't a broad cultural shift occur in which expectations are better managed towards the productivity of a 4-day work week?