The short answer is because his predecessor Louis XIV had done a very good job, over his very, very, very long reign, in empowering the absolute monarchy at the cost of the Nobles, the Parlement, and even the Clergy. Not to say that everything was perfect, but Louis XV had a really great start.

Heck, Louis XIV outlived his son and grandson. His rule was a very long period during which the centralization of power happened, at the cost of the powers of the Nobles, Parlement, and Clergy.

The two wars of the Fronde during Louis XIV's reign significantly reduced the powers of the Parlement and the Nobles respectively, to the point that private persons were no longer allowed to keep a private army.

Further, the Versailles system he developed forced Nobles to personally invest time in the Versailles system, thus depriving them the opportunity to raise an army in their own home territory if they wanted to go against the will of the king.

That's why for all of Louis XV's failings, which critiques say include:

• Diplomatic failures w.r.t. the rise of Prussia as a land power, England was international power, and the decline of Spain and Austria. In other words, the re-alignment to ally with Austria following the Austrian War of Succession went against France's strategic interest.

• Over-reach on the Parlements as he went further than weaken them, he tried to disband some of them.

• Over-use of devaluation as a means to overcome deficit.

• Over-sell of military commissions leading to military failures.

• Over-abuse of the Versailles system where it became an arena of competition between his various mistresses, factions, etc.

For all these failings, it still took until Louis XVI's reign that the people -- the ones without any privileges -- rose up against the King.

Source: McKay, Scott, The Rise of the Great Powers.