> This is so wild to me because output and work quality rapidly decline at (or well before) 40 hours a week.

I see this comment regularly here. There are lots of people who can and do work for much more than 40 hours a week, and these are productive hours. Also, it is a sliding scale of productivity. It's not like hour 41 is 100% unproductive. However, I do appreciate that most normies are probably more productive if they work less than 40 hours a week, but make those hours very focused.