Because France was bankrupt from helping the American colonists in their fight against Great Britain for their independence (The American Revolution).
They had problems with a number of its neighbors including the Russians and England that is kinda why no one stepped in during the Revolution.
When Louis had first ascended the throne, his chief financial officer was a man named Turgot who was a brilliant and creative administrator. Turgot instantly set about trying to reform the country's financial situation by instituting a series of reforms that included replacing the corvée with a tax on landowners, an easing of guild laws to allow industrial manufacturing to increase, and, radically, a sharp cut in monarchical expenses.
When the reforms failed, Louis dismissed Turgot. From that point onwards, the country would fall into ruinous financial crisis. At the heart of the crisis was the financial and administrative mismanagement of taxes. Both the Seven Years War and the French support of the American Revolution had put France deeply in debt; over one half of the country's budget was dedicated to paying off that debt.
The country was going broke.
