Economies of Scale.
People prefer maida bread more than whole wheat. Taste of maida bread makes it compatible with other secondary foods you eat with it. For e.g. jam, burji, etc. List of things you can eat with whole wheat bread is less. Some people also don't like taste of it even though it is good for health.
Manufactures want their profuct to be sold. Probabilty of wheat bread getting bought is always more than probability of buying whole wheat bread. So manufactures buy huge quantity of white flour instead of grinded whole wheat. So even though cost of maida is greater than whole wheat at micro scale but due to excessive buying of maida give leverage to manufactures to lower the price.
Whereas if you see through marketting prespective people who buy whole wheat bread are generally diet conscious. And people value medicine more than food. So even though you increase the prices buy 1-2 rupees they are going to buy that type of bread. And it also gives them social credit which are pyschological wins that even though there are other breads at lower prices they chose something more valuable for their health.
If you keep low or same as maida bread you are not going to get profitable and health conscious people will keep away from your brand because for them it is some cheap wheat bread product.
I read many comments that manufactures & seller are not regulated and are given free reign. Controlling prices did not work for soviet neither it will work for us. You have to let people decide what they are going to price their product at because if we go another way around there are some undesired consequences. In the end costumer decides wheather to buy a certain product or not. If its affordable they will buy not they will not.