Selling entire collections always go for less cumulatively than selling individual items. Of course the tradeoff is the time required to list, manage, package, and ship individual sales.
My comment about the PS4 games I've purchased and subsequently sold is in reference to individual games.
There are a number of games that I purchased the physical game,but then didn't enjoy it and sold it for more than I purchased it for.
There are a handful of instances where I purchased a physical release and never opened it. ...then months later the digital copy went on sale for dirt cheap, like $3.99, then I sold the physical copy for more than I paid initially,so it covered the digital purchase price plus a little profit left over.
Of course there are also instances when I've sold a used game for less than I paid.
I should add, I'm not purchasing with the outlook of making any money. I hate dealing with selling. It is a pain in the ass overall.
The point is actual ownership of the item I've paid for - being able to trade it, loan it, sell it, play it without being online, etc.