Before the French Revolution, when a state was faced with social-economic problems such as famine, usually, it would be followed by a peasant revolt that demanded better treatment, or, a pretender from a rival noble family of the established dynasty using the outraged masses as a tool to overthrow the king. But this was not the case in the French Revolution, for instead of a simple huge peasant revolt it was a revolution that was first of it's kind that torn the entire old order. Why is that? If we looked at the situation of Europe at the time, it seemed that the republics like Venice and the Netherlands weren't doing well at all compared to their absolutist counterparts(Except for France of course), so why is that amidst the states of enlightened of absolutism, republicanism became so widespread to the masses when it was such a new concept for most of the French at the time, and that the French Revolution was what it was, and not the aforementioned usual peasant revolt or pretender rebellion?
There are a wide variety of theories on exactly why the French Revolution happened and went the way it did. There is no unified theory on this, so you may find some disagreements.
A contributor to the shift in politics was economic. France was technologically advanced in many areas, and with increased manufacturing technology grew more wealthy French individuals. Adam Smith had published his Wealth of Nations and free market ideas were growing in opposition to feudalism. Now, going back a bit: King Louis the XIV had made offices purchasable (venal offices), so that any French individual could dish out the money to buy a seat in government. Many of these newly moneyed people, who came from the third estate (not nobility) instead of the second estate (nobility), were the ones buying venal offices. Aside from the obvious tax exemptions and other privileges, many took venal offices because it was possible to rise to the nobility after so many generations.
The old guard nobility looked down their noses at the newcomers, though. The old nobility were also generally declining in income, contributing to the resentment aside from the perception of "true nobility". So how did this effect the masses? Well, the old nobility were much more relaxed in their positions and weren't as controlling to their tenants as the new guard. When the National Assembly formed at the beginning of the Revolution, these tensions dragged noble privileges to the center of the debate. In the end, the side of the assembly more opposed to noble privileges won out. Basically, the French nobility were in a crisis on their own, unrelated to the masses.
While the nobility were undergoing these tensions, guess who suffered the most? That's right, the poorest. While the nobility and aspiring nobility were doing their thing prior to the revolution, conditions for the peasants were only getting worse. Taxation was largely regressive. Tax collectors would arrive constantly and incessantly, often asking for the same taxes which were already paid. On top of this, France had experienced massive inflation, so work could hardly earn enough to keep people alive. This, while a new breed of bourgeoisie landowners are coming in and bossing them around. They're barely able to eat while the wealthy are eating just fine. Eventually, they have to wonder whether this feudal nobility system is even worth preserving.
Then you have the ideological influence. The American Revolution happened only 10 year prior and was a massive success. Republicanism and other liberal ideas were increasingly common to the French people. Printing political pamphlets was easier than ever and there were more books in circulation than ever before. Then you have a press eager to publish wild conspiracy theories about key figures in France. This is a recipe for people wanting to be totally rid of the monarchy and nobility.
It comes to a head when food shortages, inflation, and the debt crisis all combine. For many, the burden was unbearable. They felt they had little to lose but everything to gain fighting for these ideas, so that's what they did. There was no absolute ideological consistency, but the "sans-culottes" as they were called were in favor of a government which gave them more liberty and equality. They just felt that this couldn't be obtained so long as the monarchy and nobility continued.