I think it's the trees. I have a pair of JLs here that are about eight years old, and I've worn them maybe one or two times (bought new, not second hand, not factory seconds, etc). Also have a number of EG shoes that I only wear maybe once every two or three years. They also have the same issue.
I don't think anyone would argue against the idea that you run into serious diminishing returns. The difference between using no trees and generic trees is obviously bigger, and represents more value for your money. It's just a question of whether you want to spend that extra bit to not deal with those minor issues. Seems totally dependent on each person. I'm just saying the effect is there.
Edited by dieworkwear - 7/3/16 at 12:35pm