First you have the location: the hotel is in the ultra-exclusive Place Vendome. The hotel’s neighbours include the world’s most expensive jewellers and the jewel of the Paris hotels: Le Ritz itself. The Louvre is only steps away, as are the Opera, the Tuileries, the Concorde and the Madeleine.
Then you have the rooms. They are bigger than in most hotels of this standing, some (like the Mansart suites) are trully ‘grandes’ and even grand, if combined together. The Vendome suites are also good-sized. They are very quiet and have kept a veneer of charm and class from a time when travelling was obviously done more leisurely and when comfort meant having more space. Most rooms offer views of the creme de la creme of Parisian boutiques.
Finally you have the price. While not the cheapest hotel in Paris, it is undoubtedly one of the best price/quality ratio that can be found either on the Left or the Right bank.
So, if you chose to not got to the Mansart, it would be either because: 1. You have family in Paris and you do not need to stay at a hotel, 2. You cannot stand the place Vendome and you wish to be as far away from it as possible, 3. You like to overpay when staying at a hotel, or 4. You’re planning on paying your hotel stay with Frequent Flyer miles.