Some items, especially for third parties, disposal is determined by the third party. This means if the item is not selling well and the third party (amazon has lots of these) doesn't want to or is not big enough to go through the liquidation approach, and doesn't want to pay storage fees and penalties for slow sales.

Other products are not selling well.

A retailer may go through a liquidator if the quality of returns is high (mostly new in box). You'll see people flipping this stuff on ebay all the time.

For premium brands there may be restrictions on resale to avoid devaluing the retail brand. Or they'll only sell in store for physical pickup (outlet style etc).

In the end calculation are made, cost to process, sort, return, restock, liquidiate etc. For items $25 or less it can quickly be not worth it to cycle the product. Especially if there ends up being scuffs and dings on the instore product etc (shoppers are rediculously picky sometimes).

That said, if this is hard to find items, they usually find a good market (returned AMD processors etc).