The Brain Shop

Our sleep-wake cycles are governed by internal clocks in our brains, obviously connected to other clocks in the rest of our bodies. It’s like an internal orchestra.
The period (time needed to complete a full revolution) of our sleep-wake cycle clock is close to 24 hours but not quite that. It’s actually slightly longer. That is why we need a daily “entrainment” from natural light to reset our clocks to the external (geophysical) time.
It is well known that as people grow older, they tend to wake up earlier. One explanation is that their internal clock controlling their sleep-wake cycles changes with age; its period becomes shorter, which means the frequency of the oscillations increases; that is enough to change the phase relation between the internal clock and the external (“real”) time. It’s a fact documented in golden hamsters (a preferred mamal chronobiology model for decades) and presumably other species too.
In humans, early awakening is a problem for many reasons. Remember the elderly gentleman who wakes up before dawn to count the silverware in his home to make sure nobody has stolen one his his spoons? Yes, early awakening may be a sign of more than one illness.
In human societies, traditionally the ones in power have been individuals of advanced age; this is not so often these days; additionally, alpha males are known to be more aggressive than the average in primates; aggressive behavior in mammals is associated with more regular sleep-wake cycles.

Among primates, and humans are no exception, to hold their power, the dominant individuals need to systematically oppress their orderlings. Since early awakening is a common feature in old age, a good use of this feature by the dominant males is to force others to wake up early too. That way what is basically a health problem becomes a virtue and also a mechanism of domination. They can force all their subordinates to be at work before dawn. That helps them look responsible, hard working and productive. It’s also a way to infuse a sense of defeat on the ones in the lower ranks.
So, here is the answer why so many institutions have a mandatory early schedule. Our leaders set an example of virtue and work ethics by showing up at work earlier than everyone and obviously forcing everybody else to do the same. Only recently some voices have been raised to question the early schedules in schools, for example. However, popular culture (which is usually shaped by the dominant groups) still maintains the traditional association between early rising and hard work, virtue and honesty.