S'obvious, innit? It's to maximise the amount of daylight you have available during your waking day. Makes more sense to have more in the evening, if the more you were getting in the morning you were sleeping through. No one wants it to get light midway through the morning in winter, or dark early in the evening in summer. That's a bit of a bore in the tropics. 6pm and it's all over for the day. I like the 10 pm BBQs.
Psychology, innit? If the government told everybody to get up an hour earlier every morning from March to October, hardly anybody would obey. So the government decides to put the clocks forward an hour from March to October, it has the same effect, and nobody minds.