Final answer:
The Enlightenment thinkers reached their height of development in France due to the patronage and support of the French monarchy.
Step-by-step explanation:
The Enlightenment thinkers reached their height of development in France due to several reasons, but the most significant factor was the patronage and support of the French monarchy. The French monarchy, particularly during the Bourbon Era, embraced the ideas of the Enlightenment and provided financial support and protection to the philosophers. This allowed Enlightenment ideas to flourish and spread across French society.