It goes through cycles naturally and from time to time the magnetic poles flip (it happens every few hundred thousand years). The magnetic field is largely created by the movement of molten iron and nickel in the earth's outer core. Wikipedia has a pretty good article on it.[0]

[0] https://en.wikipedia.org/wiki/Earth's_magnetic_field

>> The article mentions that the magnetic field of the earth is changing more rapidly. Why is that?

It is heading toward Russia. Putin is a super villain and he's stealing the north pole.

No one knows. We just observe it happening.