France owed monstrous war debts. The Seven Years War was violent, bloody, and expensive. Almost every power in the world took part. In fact, given the general state of the world at that time it could easily have been called a World War, had anybody thought of the term. It had rearranged things only slightly in the world at the time considering the enormous cost in lives and money. Either way, though, that war and the involvement in the Americas left France with crippling debt.
France was glued into an outdated way of governing. The ruling elite paid few, if any taxes. And since they were the "ruling elite" it was almost an act of treason to suggest changes. It was left to the common classes, the third estate to finance the government. And even in that it was rippled with inconsistencies, different territories paid taxes at divergent rates.
Clergy enjoyed a tax free existence and were seen to be living lavishly off the backs of the common people. The importance of the church allowed it to grow enormously profitable, owning almost 10 percent of the land. Rent and tithes made the church extremely wealthy, and glaring, gaudy ostentatious examples of this were on display almost everywhere.
According to P.M. Jones in his insightful The French Revolution 1787 - 1804 "However, there was also a principle at stake, for the three-tier division of ancien regime society into ‘estates’ turned ultimately on the question of exemptions. Direct taxation was demeaning and to be liable to it was an
unmistakable sign of baseness. Bringing the clergy and the nobility - not to mention sundry other groups - into the tax net might make perfect economic sense, but the social implications were enormous." Clearly, nobody was in a big hurry to change the status quo.
When weather conditions caused poor harvests food prices skyrocketed it was akin to storing the gasoline and matches next to the fireplace. Combustion was almost unavoidable. And when it ignited it burned across an entire continent.
Of course, it would be foolish to claim these were the only factors. The fervor of the American Revolution was intoxicating. An ancient system of societal division (the ancien regime) was chafing in times of mass communication, provided by Gutenburg was bound to unravel. But, these things would likely have been slowly incorporated into the fabric of the nation.
Crushing debt, a government unable, or unwilling to make the changes needed, and a powerful, uncontrollable religious authority making obscene profits while the working class struggles to provide the most basic needs is obviously a recipe for disaster. Of course, that was then.