What leads to Polaris not always being the North Star?

The reason Polaris is not always the North Star is due to axial precession, which is the gradual shift in the orientation of Earth's rotation axis over time. Earth's axis is tilted at an angle of about 23.5 degrees from the perpendicular to the plane of its orbit around the Sun, and it wobbles like a spinning top. This wobble causes the orientation of Earth's axis to trace out a circular path over approximately 26,000 years.

As a result of this precession, the pole stars change over time. Currently, Polaris is aligned closely with the North Celestial Pole, making it our designated North Star. However, thousands of years ago, other stars, such as Thuban in the constellation Draco, were the North Star during different periods due to this gradual shifting of the axis. In the future, other stars will take on this role as well, as the precession continues unabated.

Therefore, it is this phenomenon of axial precession that ultimately leads to Polaris not always being the North Star, confirming the choice as the correct answer.