It also has to do with legislation and with marginal value. Above 40 hours or so, a lot of countries have laws, like overtime pay and what have you, that start

It also has to do with legislation and with marginal value. Above 40 hours or so, a lot of countries have laws, like overtime pay and what have you, that start to kick in and make it less worthwhile for an employer to ask for those hours. As well, most people find that above that amount of time, the value they get from increased income starts to go below the value they get from non-paid-work time. It's sort of a normal equilibrium.