Too glib; they've been holding pretty steady at 8 hours, mainly due to regulation. Other work has increased hours, such as in many areas of health care, for example. Many folks also patch together multiple jobs in order to achieve a livable income and can work upwards of 12-16 hour days. I know several, personally.

Keynes predicted we'd be down to 3 or 4 hours a day by now, but that never happened due (partly) to the ever-increasing competitive ability/imposition that technology allows managers and shareholders to impose on labor in an effort to maximize economic potential and productivity.

They went down thanks to major labor laws.

Even now, average working hours in developed nations are above the "legal norm".

Though the automation definitely helped to make it more feasible to work less, there is still a political fight to be had to push the hours down even more.