When a reaction has 4 gas molecules as reactants and 1 gas molecule on the product side, in order to make the reaction go to the left (reverse), why does it have to run on low pressure?
When the pressure decreases/is low, the system will try to counteract the decrease in pressure by shifting the reaction to the left to produce more gas molecules, which exerts more pressure, thereby restoring equilibrium.
From a distance, Le Chatelier goes for all other points in a reaction the same way as well: from high to low. If you get one side low in pressure for instance, you're implicitly getting the other side "high", from high to low the direction reverses then😉
Remember it from social governance of a society: from rich to poor is good and universe actually is telling this all the time 🙂