I can think of two compelling ones.
I am currently selling a Tele Vue eyepiece which is one of the finest ever made, it is brilliant, and in extremely good condition, and for no other reason than just lack of use, preferring binoviewing for the last 7 years or so.
It is just too much money tied up without use.
I, like so many of our colleagues on this forum, just love buying and trying eyepieces. I still have too many and so I choose to sell when I want to fund something else.
I do agree that it is possible to be disappointed with the actual condition of a piece of kit against the description offered, but that has rarely happened to me, and certainly, never from anyone on this forum....