[jcattle]

Because due to rotation the earth bulges outward at the equator. The actual term is "Equatorial bulge".

Due to that "equatorial bulge" you are further away from earths dense center, than at the equator. And due to the inverse square law, you lose intensity of that gravitational force very quickly, the further you are away.

Hence: the smallest gravitational force you get is on a mountain in the Andes near the equator.