Chocobo racing has more MGP return than Triple Triad imo. Also the Cactpot needs to be brought into consideration, everyone has the ability to receive 1 million MGP if they match all numbers, if the prices were reduced then a winner of the Cactpot will be able to buy everything in one go.

The Gold Saucer is staying in Eorzea, it is not going away so there is no need to reduce the cost of items because it's suppose to take time.