The rider gets no help because no one wants to aid the aristocrats.
The French Revolution was an intense class struggle. The peasants had been mistreated and taken advantage of for years, and they were sick of it. To them, the wealthy aristocrats were fed off of the fruits of their labor and they got nothing in return.
When there is a fire at the chateau, you can see why the Marquis would not have the villagers’ sympathy. Good riddance to the aristocrat, as far as they are concerned. He has never lifted one finger to help them, instead taxing them into extreme poverty. Thus the "rider" from the chateau gets no help when he desperately asks for it.
At the gate, a group of officers were looking at the fire; removed from them, a group of soldiers. "Help, gentlemen—officers! The chateau is on fire; valuable objects may be saved from the flames by timely aid! Help, help!" The officers looked towards the soldiers who looked at the fire; gave no orders; and answered, with shrugs and biting of lips, "It must burn." (Book 2, Ch. 23)
Note that he is concerned about “valuable objects.” Sure, save the property. None of the villagers have any valuable property. Monseigneur took everything they had and left them next to nothing. They can get at least some small satisfaction in his destruction.
Gabelle was just doing his job. Although he was the collector of the hated rents and taxes, the village was in his care. He was basically a middle-man. To the revolutionaries, he was also not much more than a pseudo-aristocrat. He did the Marquis' bidding.
Revolutions do not start overnight. It takes a series of abuses that make people believe that they have nothing to lose, and everything to gain, from ousting those in power. Dickens is careful in portraying the nuances of why there was a revolution, as well as the atrocities of the revolution itself.