I think there are several reasons for this.
They are expensive so some guys sell because they need money and can get a good chunk by selling an expensive item that holds it's value.
There are alot of them around so there will be some for sale.
Updating a power or reticle choice, selling old to buy new scope with desired reticle, zero stop, high speed turrets etc.
I sell alot of things because I want to try something else and only have limited funds for new purchase, so something must go. I would rather have a few really good items than a bunch of cheap ones, but I have a friend who has a whole safe full of junk and is happy because he likes quantity, I like quality.
I definitely don't think most are selling because they are not satisfied because these scope bring top dollar used.
Gary