When the industrial revolution happened people thought we'd have a lot more leisure time. Oops
Standard of living changes. Also, you need the money to own the means of production for it to work for you.
Not working would also lead to social decay. People need a reason to wake up in the morning, and something to strive towards. I've met a lot of dopey retired people who do nothing all day, it's not good for the mind or body. Some of them spend their time on message boards
Times of plenty create soft people, as the saying goes.