The world is ruled by aliens. And they demand things from us. A lot of things. And they are never satiated - they want ever more things. Always more.
They do not seem to care what these things are. Only that there's a lot of them, and that they are the end result of a long manufacturing process - the longer the better.
If we do not live up to this quota of massively manufactured mass productivity, these aliens will eat us. They will begin with the children, and then work their way up the age groups. Eventually, we will all be eaten by our alien overlords, a fate worse than death.
And certainly worse than you average workday. To be sure.
This is the one explanation I can find to why there is still a widespread insistence on everyone working at full capacity at all times. Should one look at the rate of productivity increase, one would conclude that we've already passed the point where we produce all we need and will ever need. Should one look at the increasing rates of unemployment, one would conclude that unemployment is a permanent feature of the modern economy (and cannot be otherwise, given the aforementioned productivity increases). And should one look at the ever more creative and sadistic ways of punishing those who happen to be unemployed in an economy that neither want, need or afford them - one would conclude that someone has a deep seated hate for their fellow human beings.
Given all this, aliens is the one reasonable explanation. They will eat our babies if we cut ourselves and the planet some slack, and it is indeed the very end of humanity if you don't show up to work eight hours a day five days a week forty years of your life.
It is the one explanation that makes sense.
You rarely get to say that about aliens. But given the state of the economy - why not?