90% of keyboards I see for sale, have either scratches, dings, or both. Even the aluminum ones which are supposedly tougher have them. I have no idea why they always have surface damage, unless the previous owners throw, knock against walls/corners, drag on rough surfaces or smash them out of rage.
I have carried and transported my keyboards several times in the past and none of them have sustained any damage, and I wasn’t even trying to be ultra careful with them. It seems so hard for me to damage keyboard cases unless I intentionally do it, therefore I really don’t understand how people manage to ding or scratch their boards.
Some people just drop stuff a lot… and drop things onto other things a lot. Some people just use them as tools. Some people sit for hours cleaning them with a blower brush then display them. It takes all kinds. We’re a broad church :) I don’t agree with your 90% figure though.