The reason for this social dynamic is that we live in an ideals based culture, but a binary reality, where opposites create both balance and tension. Without the ups and downs, it would just be a flatline.
As mobile organisms, we assume we are going somewhere, but ‘every action has an equal and opposite reaction.’ While it is a complicated process leading to the political polarities of today, let me paint this with a very broad brush;
Think of reality as a dichotomy of energy and the forms it manifests. Galaxies are energy radiating out, as form gravitates in. As organisms, we have the digestive, respiratory and circulatory systems driving us on, along with a central nervous system to sort through the information produced, internally and externally. Motor and steering.
In society, we have those raw organic energies bubbling up, along with cultural and civil forms coalescing in, not only giving focus, structure and coherence, but having to select which desires to encourage and which need more management, if not outright suppression.
Liberalism can be loosely associated with the social energies, in all their myriad expressions, while conservatism equates with the forms and organization.
Obviously this simple binary has many shades and colorings, but if we really want to understand the dynamic, it is something that needs exploring. The middle ground is a battlefield otherwise.