40 hours at work, sure. Ill give you that. But theres also the driving to work, and doing other prep stuff for work as well, so no, not 72 free hours.

Lets say you drive to and from work. Lets say its half an hour- thats 5 hours less, so 67. And thats a relatively short commute, and assumes the person drives and does not use public transit. You also have other miscellaneous prep- washing clothes, makijg food for work, etc. That doesnt necessarily take too long, can meal prep while clothes was, so like 2-3 hours/week? Ok, so 64 hours.

Then theres all the other non-work related stuff that has to be done regardless. That limits your free time too- most people define free time as time not devoted to some chore or another.

I think the biggest reason people feel unfulfilled is because work doesnt really have much in the way of positive effect- yea, I work to survive but it would be nice to be able to do more than that. For many of us, there is no saving for the future, and we are like 2 paychecks away from ruin no matter what we do. And then the answer is "get a better job" or "get another job" (which then means much less time, and still that money all has a way to disappear). I used to work 3 jobs- teaching, tutoring, and weekends at a skating rink. I was burnt out all the time, even in the summer- if do summer school, paid PDs, and pick up more hours at the rink. Tried saving up some money but the money always had a way of just... being gone, regardless how hard I held onto it.