Here's why:

* Domains: A magnetic domain is a small region within a magnetic material where the magnetic moments of the atoms are aligned in the same direction.

* Random Alignment: In an unmagnetized material, these domains are pointing in various directions. The magnetic fields of these domains cancel each other out, resulting in no net magnetic field.

* Magnetization: When a material is magnetized, an external magnetic field forces the domains to align in the same direction, creating a strong magnetic field.

Think of it like a bunch of tiny magnets pointing in different directions. When they're all jumbled up, they cancel each other out. But when you align them, they create a strong magnetic field.