Here's why:

* Magnetic Field Lines: Magnetic field lines represent the direction and strength of the magnetic field. These lines are densest and closest together at the poles of a magnet, indicating a stronger magnetic force.

* Concentration of Magnetic Charge: Magnetic poles are where the magnetic charge is concentrated. This concentration creates a stronger magnetic field in those areas.

Think of it like this: Imagine a magnet as a bar with two ends. The ends are the poles (north and south). The magnetic force is strongest at these ends, just as the gravitational force is strongest at the center of the Earth.