>>11770037That only happens in objects with different moments of inertia in 3 axes, where the rotation occurs along the axis with the middle moment of inertia. Planets naturally only have 2 moments of inertia because their spin causes their equator to bulge outwards in every direction along the plane of the equator. Taken to an extreme, a planet has moments of inertia similar to a disc.
It's possible that an irregularly shaped planet could experience it, and it likely does happen to planets early in their formation. But planets are not static objects, and over time the centripetal force of their spin will naturally force its equator into uniformity, and they will eventually become stable.
