The reality is people are common lazy and will only be productive for only a portion of hours per week. Allowing and having them work more only equals to lack of productivity. Very simple, you get more work having two part timers over one full timer = say that the cumulative hours equals 40 hrs per week.
Corporations and business models have such a thing per employee according to some FTE computation. Say you have one person work is paid 8 hours a day. While they're actually at work for 9 hours a day with an hour lunch in between. The FTE is something like 6 = meaning it is expected to get only 6 actual work hours of productivity. So 6 FTE times 5 work days out of the week is 30 hours. So why waste a person's time of 9 daily hours times 5 days = 45 hours out of their life.
Just have them come in, do the actual 6 hours of productivity and let them go home. Someone got paid like 1 mil bucks to figure this out over the course of two years, but a seven year old child could've figure it out in one day.
It's amazing how the business world works.
Long gone are the days where real working workers stay productive OT. It's a dying breed.