Acceleration due to gravity depends upon the mass of the planet (M) and the distance between the center of the planet to the center of the body (R).

$$\rm g \propto M \ and \ g \propto \frac{1}{R^{2}}$$

The mass of the Earth is a constant quantity and does not vary from place to place.

The earth is not perfectly spherical. Its radius is more at the equator than at the poles. Hence, the value of R varies at different parts of the earth. Consequently, acceleration due to gravity is not the same in all parts of the earth.