The Economics Of Hardware

I'm working on a DIY repair and in doing so I am reminded of an odd little economic reality:

Finding the part that you need to make a repair that has a major effect on the value of your entire project is not infrequently very difficult. It can take days, visits to multiple stores, and hours scouring the appropriate section of each store. But, should you be graced with the good fortune of actually finding the particular part that you need, without having to buy a lot of parts that you don't need in a set to go with it, the price of that nearly impossible to find part is often a pittance.

I'm not sure why that is so. Why don't hardware stores charge high prices for obscure parts and carry wider inventories of them so that they are easier to find?

But, it seems to be the reality.