Here's why:

* Earth's Tilt: The Earth is tilted on its axis. This tilt means that during the winter in the northern hemisphere, the North Pole is tilted away from the sun, and the sun's rays hit the Earth at a very shallow angle. The same applies to the South Pole during the southern hemisphere's winter.

* Angle and Intensity: The lower the angle of the sun's rays, the more spread out the energy is. This means that the intensity of the sunlight is much weaker compared to areas closer to the equator.

This low angle of solar radiation is a major reason why polar areas experience long periods of darkness, cold temperatures, and have unique ecosystems adapted to these conditions.