Microsoft does not publish rationale articles about how or why they designed things in a certain way. There are dozens of things like this about Excel (maybe hundreds) that Microsoft has never explained (e.g., why certain functions do not work when referencing a closed workbook). I know how charts work based on 30 years of experience using Excel. If you want more of an explanation I'm afraid you will have to do an internet search for specifically what you are looking for. Or perhaps perform a series of experiments until you can predict the behavior.