Question

The value of g is greater at the poles than at the equator why​

Answer 1

because the gravitational pull is maximum at the poles and decreases as it comes down toward the equator.

Answer 2

The reason is because the Earth is not a perfect sphere. The distance from the poles to the centre of the Earth is smaller and the gravity is slightly greater.
The distance from the equator to the centre is slightly bigger so gravity is slightly smaller.