Solarpunk

The set of environmental conditions is different in each country, and indeed for each individual human. The level of technological advancement only comprises a small piece of that picture.

Because of the recent rapid technological advances in the past century, essentially every society worldwide is struggling to adapt to the new technological landscape. But due to all of the other contributing factors, the struggle is slightly different for everyone.

Just looking at the average work hours is a miniscule people of the puzzle. How much money are people making in exchange for their time? Do they have to pay for Healthcare? What types of jobs are most common? What is the historical context of the population that has led them to this point? Were they working more or less 100 years ago? Did they have more wealth 100 years ago? What is the current rate of mental illness and disability? What is the historical and current prevalence of religion?

You could continue with questions in this vein more or less infinitely. And the answer to each question would vary substantially depending on the nation/community/individual that you chose to focus on. And each answer would potentially have an impact when trying to analyze how the current culture came about.

To answer your single hypothetical question, I think one of the primary contributing factors to the reduced working hours for many wealthy western European countries when compared to the US is the relative level of financial and social inequality along with the taxation rate. For France et all, the tax rate is significantly higher and the level of social support is correspondingly higher.

This reduces some of the necessity of working more hours, because the variability of income is reduced. If low-income people still make enough money and have enough benefits to make a decent life, they don't need to work so many hours just to survive. Also, high-income people will have a reduced incentive to work so many hours because the overall financial benefit is relatively smaller when compared to the US where you can avoid taxation to a much greater extent.