The villagers did not try to control the fire because they hated the chateau and everything it stood for to them. It was associated with the unfair rents they paid, the poverty of their lives and the injustice of their treatment. The chateau represented the Marquis who had not even accorded them status as humans and treated them worse than his animals. Fighting fires was hard work. Why should they work hard to save something they saw as a symbol of oppression?
The fire here is also symbolic. The villagers could no more put out the fire destroying the chateau than they could put a halt on the revolutionary fires that would eventually overtake their country and destroy thousands of innocent lives.