I don't have room to keep empty boxes. I used to keep other, unrelated items inside some computer boxes, but lost track of a few items, so I gave up on the concept of keeping boxes at all.
As above, I will keep a box until the return period is past, then out it goes. I don't see the point in keeping (at least for me)
I also don't purchase any item of tech with the idea of eventually selling it. I use it, until I am done using it. Sometimes it is just all used up.
I have had maybe 15 different Macs during that 25 years. I have never sold one off (and only have 5 or 6 now that are still useful to me. I lose count 😀)
I guess I am unusual, but I have never had a later need for original packing materials in more than 25 years of working with computers, and other tech - even during a move.