I used to sell gear on the boards, sometimes the same items back to back. Having the lens boxes would always sell first and at higher prices. It just is, whether you find it incredulous or not. Some people have a psychological need to have everything that came with the gear they buy, whether they think it means it wasn’t stolen goods or it might have been taken better care of if the person has the box.
I can’t answer that but I, and many others, know that having the boxes makes for better sales. There are many articles that also talk about this. Finally we have discussions about this for years, the topic pops up time and time again.
I guess I would have to ask, “who cares”? I keep my boxes to sell with the gear, and I have sold boxes to others, and then there are those of you that don’t see a need. There is no right or wrong answer, so do what you want. I will continue to keep all my product boxes and when I sell, great for the buyer, and for me.