I think it is because the left argues in emotional terms, not necessarily rational. When cornered, they retreat to what they know. Emotion.
That’s true. People on the Left frequently revert to emotion as a means of argumentation because their ideology is largely feeling-based. It further leads them to argue from a normative point of view (what should be) as opposed to an empirical one (what is) and also to invert cause and effect in order to avoid unpleasant realities.