I realize this is a broad question which likely doesn't have one answer, but I find myself interested in hearing more about it and thought it might result in some interesting discussion. Didn't see it in the popular questions list and don't remember seeing it discussed before, so hopefully it's all right to ask!
The centralization policies of the later Bourbons were key. Louis XIV didn't trust the old nobility and effectively forced them to live at Versailles, where they were expected to compete with one another for the privileges of attending the king when he woke up and got dressed, eating with him, hunting with him, etc, while middle class bureaucrats and clergymen like Richelieu and Mazarin actually ran the country. Their estates were taxed at a very low rate, but they could no longer maintain private armies and their fortified castles had to be raised or converted into palaces.
The competition at Versailles also involved dressing in the best clothes and throwing the best parties aned dances.
See, for example Louis XIV's Use of Fashion to Control the Nobility
One of the removed replies in this thread linked to an NPR story that I wanted to listen to, but did not save. Does anyone have that link?