The poles receive more direct sunshine so it has to do with the angle that the light hits. The Earth is round and when light hits it the light wraps around the earth. At the poles the light is very stretched and at the equator it is very direct hence it is hotter at the poles.
Located almost due east of the Reflecting Pool and the Lincoln Memorial, the monument, made of marble, granite, and bluestone gneiss, is both the world's tallest stone structure and the world's tallest obelisk, standing 554 feet 7 11⁄32 inches (169.046 m) tall according to the National Geodetic Survey