You work more than your ideal amount. Equivalently, you value your free time at higher than what you get payed. Presumably, people like you mixed in with people who want to work longer averages out to free time being worth the same as what one gets payed.

The marginal utility of an extra hour of free time outweighs my nominal hourly wage. My point is that most skilled jobs offer limited flexibility in the marginal substitution of additional free time for income. One reason for this is that most skilled jobs have an annual salary, not an hourly wage. I would prefer to work 10% or 20% less for 10% or 20% less income (which given progressive income taxes would actually amount to a cost saving of more than 10% or 20% to my employer) but there is limited flexibility to negotiate this in many jobs. Believe me, I've tried.

It's possible that I significantly underestimated the decrease in marginal production as you work longer. Perhaps after eight hours, each additional hour people work is only worth minimum wage.

In my industry (software development) numerous studies have found that productivity flattens off beyond 40 hours a week and actually declines beyond about 60 hours a week (more mistakes are made and morale is impacted). Unfortunately management doesn't always appreciate this fact. And again, reiterating that many skilled jobs are not paid on an hourly wage and do not pay overtime, there is no direct trade off between hours worked and income for many skilled employees.