Taken together, many people with a problem solving mind see those involved as wallowing in their own failure. A natural response to such behavior is revulsion.
1 - http://lifehacker.com/working-over-40-hours-a-week-makes-you...
Of course, if you are self-employed, there is no way that those rules can be enforced… but it will be frowned upon by your relatives, because we know that it is wrong in the long term.
(I moved to work in Paris this year, so am rather interested... though I believe my 'cadre' status exempts me from this anyway)
That's the part that I find crazy.
Other reasons are work/life balance, enjoying time to relax, spending time with friends or family, mental health reasons, and things like that.
The vast majority of salaried employees see no change in quality of life if they work 35, 40, or 45 hours one week to the next. In fact, if you work a lot, one would think you're less likely to go out and spend your money in your limited free time.
The times I've worked 60+ hours a week have always been better for my bank account than the times I've worked 35-40.