Edit: people replying seem to think that I'm saying that:
1. only Amazon does this; 2. it can be prevented but Amazon just chooses not to.
I didn't say any of those things.
I mean, what do we want to happen? These things to sit idle forever in a warehouse taking up space?
...and that's how you end up with shortages.
You can only give away the stuff you "could" sell but can't find a buyer for, which (1) pretty much means no one wants it and (2) will poison your relationship with the people who sell you the stuff you *can* resell!
What, you tried selling a made-for-landfill thing that works half the time? Should've done your research. Choose your loss.
This implies those providers can dispose of the unsold inventory how they see fit, possibly by selling it wholesale or for parts, etc. This doesn't seem like a huge crime.