Well, I can only speak for myself, but I have to disagree.I think people who do that see the item solely as an investment.I have always thought it was weird to keep stuff in it's packaging. I understand people do that to make money off them but if you are just going to sell, what's the point of buying in the first place?
I.E buy a special-print vinyl record for $30, keep it in the package, and two decades later it's worth $1000. People stick to things they're interested because they know a lot about it and can make educated guesses as to what its appreciation will be.
I don't necessarily see the few items I own as an investment, I mostly like having them. I like displaying them (livingroom space allowing). Of course I wouldn't rule out selling some of the more limited collector's editions of video games or merch I own, but only if the value increases very, very substantially and I certainly don't plan to do so when I'm buying them.