No say you estimate that you will sell 10 items of "less common size", you stock 10 items, and hope that you sell all of them. You end up selling 9, you have a remaining 10%.
How does that make a difference?
If you start a sentence with "so what you are saying", and then say something obviously silly ...
The argument would be that it's a large burden to have to write a report if you forage 10 mushrooms and toss one away.
Low volumes, higher fixed costs.
It would be very expensive for the global factory to customize the distribution of sizes manufactured for a retail store in Des Moines, Iowa. The order is tiny and it would require customized logistics, all of which greatly increases cost and complexity.