> At the end of the 19th century, anarchist thinkers predicted with modern techniques we'd be down to 10h weekly work

Similarly, John Maynard Keynes, who probably had access to better data, predicted that increased productivity would allow us to work 15 hours / week by now. And his projections for productivity growth were accurate—however the benefits never materialized.

You see something similar with women entering the work force. It used to be that married men worked 8 hours a day, and that provided for their wives, who stayed home and took care of children, etc. Then it became more common for married women to work as well. You would expect that this would mean that husbands and wives would split the work and do 4 hours/day each and likewise share domestic responsibilities. But that's not what happened. Instead men still work 8 hours a day, and women work nearly as long and also bear most of the responsibility for childcare and the home.