People (and some old people now, but not as much) used to work so monotonously and hard because the materialistic pleasure cloud we ride on today didn't really exist back then.
People's minds and their reward system was based more on a "meta-level" in regards to the physical plane, they received gratification from their work but not necessarily pleasure; that's why people used to be more spiritual naturally in all cultures of the world.
People like dirty hippies strive for this same thing in modern day, but few achieve it, or if they do experience it they don't delve in nearly as much as people used to. The only people now who still experience such a life are third world subsistence farmers, but even they have access to pain-relieving things such as modern oral hygiene.