That's kinda the thing. The five day work week evolved in response to factory work. The machines were the expensive overhead, and profit was maximized by keeping them going for as long as possible.
The work week had previously been six days, or even seven if management was insufficiently religious. Just getting down to five was a literal fight:
Office work inherited that ethic, but without the reasoning. Nobody even tried to determine the optimal number of hours.
Service sector work is more complicated, since it's often part time or hourly, and varies widely from place to place and person to person. Optimizing that would take a whole lot more work. But for office jobs, it's long since past time to reconsider why we're basing it on factory jobs.
The work week had previously been six days, or even seven if management was insufficiently religious. Just getting down to five was a literal fight:
https://www.history.com/topics/19th-century/haymarket-riot
Office work inherited that ethic, but without the reasoning. Nobody even tried to determine the optimal number of hours.
Service sector work is more complicated, since it's often part time or hourly, and varies widely from place to place and person to person. Optimizing that would take a whole lot more work. But for office jobs, it's long since past time to reconsider why we're basing it on factory jobs.