> machines produce everything we need
There's a difference between need and want. People want iPhones, but they don't need them, so they can decide themselves whether working more is worth it.
On the other hand, people need food. The only choice is work or die, which isn't really a choice. There is an infinitely large jump between extremely cheap food and free food (and energy/shelter). As food gets cheaper, wages decrease as well, so you still need to work about as long to survive. When/if food becomes free, people won't need to work any longer.