Why does location change day length?

Answer 1

It's because the Earth's axis is tilted. If the axis were perpendicular to the orbit, daylight would last 12 hours every day, pretty well everywhere on Earth.

Because the Earth's axis is tilted the amount of daylight depends on the latitude. Try to visualize the Earth rotating around its axis; when the north pole points away from the Sun, the Sun is always below the horizon from the point of view of somebody at the north pole. For somebody at the south pole, the Sun will always be above the horizon (at that time of the year). For locations in between, the days get longer and longer as you move - in this example - from the north pole towards the south pole.