Maybe it's for the same reason cinema ticket prices are the same for every movie. Price is a (often inaccurate) signal of quality. By lowering the price you are

Maybe it's for the same reason cinema ticket prices are the same for every movie. Price is a (often inaccurate) signal of quality. By lowering the price you are saying this product is inferior. On the other hand it could be because if restaurants have a similar product at a lower price, then customers might go for the cheaper option, thus reducing overall profits.