Why are the responses in the fight-or-flight system so widespread and lasting in the body, but activation of the parasympathetic nervous system is discrete in comparison?

Because responses to the fight or flight system occur through adrenaline, while adrenaline production is not stimulated in the activation of the parasympathetic nervous system.

Explanation:

The escape or fight system is activated when we are in a situation of extreme danger or stress and our body wants to get away from that danger as soon as possible. To get you out of danger quickly, the escape or fight system stimulates the production of adrenaline which allows responses to this system to last for a considerable time in the body.

On the other hand, the parasympathetic nervous system is not intended to make you move quickly away from danger, or face you for protection. On the contrary, this system has the function of making you calm down and for this reason, the production of adrenaline is not stimulated here, so the activation of this system is made discreet and delicate.