Why yes! There is a reason. It was because back then the way they presented themselves was crucial for the royalty. They had to set themselves apart from the common people. To show they were more important.

What better way than dressing more lavishly than they ever could? Rose Bertin's fashion was new and innovative at the time while it was chic and dazzling, something the indulgent Queen of France adored. ( She sadly died for her impulsive buys but it was the price of beauty, wasn't it? It's how she saw it at the very least. ) And when the Queen favors you, you can expect her followers to flock in too or spread another good word of your work. She can be credit for haute couture to attention in France.