Prices of a product do not change immediately. When a product is introduced in a market, the price associated with it is generally accepted by the consumers and with the passage of time the prices become sticky. They cannot be changed readily.
Price changes are not easy to implement because consumers are not usually willing to pay higher prices for the same product. And if it is done so, then they will switch towards the substitute of that product. So the implementation of the changes in price is difficult.