Here's why:

* Magnetic poles: Magnets have two poles, a north pole and a south pole.

* Field lines: Magnetic field lines are imaginary lines that represent the direction of the magnetic force. They always point from the north pole of a magnet to the south pole.

* Interaction: Like poles repel each other, and opposite poles attract. This is why the field lines point from north to south.

It's important to remember that this is a convention, and the direction of the magnetic field is actually defined by the force it exerts on a moving charge.