How big is it, how much did it cost to buy and what is the cost to store?
An item with a low cost and high profit margin but is bulky in an expensive warehouse, you might dump it after a few months/set amount of stock is sold (or try to reduce the sale price to clear the last stock)
Something with a finite appeal, say Holiday related or related to a Sporting event you might decide to dump at the end of the season or when England get knocked out of the World cup in Round 1.
Something with a high profit margin, low cost, small, and regular sales throughout the year you might decide to keep available for a very long time, especially if you're able to combine it's storage with other items so it's just filling in a gap between them and effectively not costing you anything to store.
It's also worth remembering that some items need better storage conditions than others so may be much more expensive to store*, or might "expire" so you have to clear them within a certain time.
In short it's a balancing act based on is it worth continuing to pay and hopefully get more profit, or is it time to call it a day and write off the cost of the remaining items and their storage to date.
I suspect every company and individual has their own criteria based on things like how much room they've got in the warehouse and how much it costs.
The likes of Poundland from memory specialise in basically saying to companies like Tesco/Morrisons/Administrators of retailers that go bust "we'll give you X% of your cost per item and collect it" which means that a company might decide to clear those £5 items sooner rather than later to free up space in their warehouses knowing that at least they're not having to pay for neither the storage or disposal costs but are getting something back (even if it's pennies in the pound).
It's much the same as how stores decide when and where to reduce their stock, and why some stores will end up practically giving stuff away** after a few months, others especially that specific type of family owned hardware store that's been in business for decades (and own the building and freehold so low overheads) might have odds and ends of stock still on the shelves or in odd corners that have been there for years (or decades), because they don't need the room so it's costing them nothing to keep them and people know that these sorts of stores can be the best place to get something odd.
*Paving slabs and garden ornaments might be fine in an open air barn with little security, books and consumer electronics tend to need to be stored in a dry environment preferably above freezing and for consumer electronics often with a lot of security.
**Really giving it away - I've seen pallets of past it's use by concrete/plaster by the door with a note to help yourself (it would have cost the retailer a lot to dump it).
