Why it is less sunny at the poles -
Because of the curvature of the Earth's surface, the same amount of sunlight is spread over a larger area towards the poles than equator. Thus, polar areas are heated less than the equatorial areas and overall temperature of the Earth is lower at the poles than the equator.
Note: Cooler temperature at the poles are not caused by the greater distance to the Sun than at the equator. The difference in distance to the Sun is insignificant.
Source: Memorie Yasuda.