Come on, la Pompadour, you were raised to be put in the bed of a Minister or even the king himself by your social class, to get a foot in the high society and a hand in the government of France. Did you expect that the nobility would take it well?
True, you low birth was a handicap, but the threat you represented was even worse as the nobles saw the very often richer Fermiers Généraux put their hands on the one thing the nobles that the Fermiers Généraux didn't have, the little political influence they had left. Remember that the Sun King had smashed their power and taken most of it for the crown, they were furious that anything could threaten the little they had left.
Besides, your influence in the politics of France made us ditch old alliances for new ones and handed us a series of defeat and the loss of our colonies. And what about the money you wasted on buildings and arts when France needed it more than you did?
True, you had good tastes, brains, and courage in plenty, but you also messed up France and there was something fishy in your later relation with the king.
Les grands seigneurs s'avilissent
Les financiers s'enrichissent
Tous les Poissons s'agrandissent
C'est le règne des vauriens ;
On épuise la finance
En bâtiments, en dépenses ;
L'État tombe en décadence ;
Le roi ne met ordre à rien, rien, rien, rien.