So this is probably a little Capitalist, but isn't the reason we're not working 3 hours a day the fact that the owners of capital capture allocate investment towards technological advancements? In other words, technology is more sought after if you can allocate research towards a robot at a high up front cost with small ongoing costs.

On a macro level, I see this as a economy optimizing for technological expansion over leisure. Worker man says shitty, then pulls out his magical pocket sized supercomputer on the bus ride home at 6pm.