It's the historically-emergent standard for good reasons, because the quality of work simply goes to shit when people work too much. Burning out workers "destroys their personal lives and gets nothing in return," writes Facebook cofounder Dustin Moskovitz.
Many people believe that weekends and the 40-hour workweek are some sort of great compromise between capitalism and hedonism, but that's not historically accurate. They are actually the carefully considered outcome of profit-maximizing research by Henry Ford in the early part of the 20th century. He discovered that you could actually get more output out of people by having them work fewer days and fewer hours. Since then, other researchers have continued to study this phenomenon, including in more modern industries like game development.
The research is clear: beyond ~40—50 hours per week, the marginal returns from additional work decrease rapidly and quickly become negative.