High cognitive load or stress makes people more likely to fall back on automated habits.

Your brain has a constant battle between two areas. Think of the front part as a wise CEO and the deeper part as a factory floor. When you are tired, stressed, or carrying a heavy mental load, the CEO gets exhausted. This is when the factory floor takes over. Because habits require almost no mental energy to run, your brain defaults to these old, automated routines to save its strength.