What reason did the French have for supporting the colonists

The primary ally for the American colonies was France. At the start of the war, France helped by providing supplies to the Continental Army such as gunpowder, cannons, clothing, and shoes. In 1778, France became an official ally of the United States through the Treaty of Alliance.

Explanation:

American colonists hoped for possible French aid in their struggle against British forces. ... When news of the Declaration of Independence and the subsequent British evacuation of Boston reached France, the French Foreign Minister Charles Graver (Comte de Vergennes) decided in favor of an alliance.