[TeMPOraL]

Imagine three companies doing equivalent work in the same sector.

Company A has 3-day work weeks; it's running Monday - Wednesday and then it's inactive for four days.

Company B is like A, but instead of not working 4 days a week, it doubles the staff and has people working 3-day work weeks in two groups.

Company C has employes working 6 days a week.

You can see that companies B and C will be strictly more productive than A and they will outcompete it quickly. As for B vs. C, it all depends on whether costs associated with additional employees (benefits, etc.) outweight the marginal productivity bonus company B has over C by virtue of employees being less tired and having a life. Apparently, the costs are greater, since most companies look more like C than B.

And hence, if you switch to 3-days workweek, you'll lose to the ones who work 6 days/week.