The way it was explained to me was:
If you are a shop, your inventory costs you money, you're paying for floor space, you're probably paying for a loan to purchase the stock. If you have an item that isn't selling, its making a loss. You have no emotional attachnent to the gear. You're better off dropping the price and getting rid of it and buying something else with the money, that's more likely to sell for a profit.
If you are an individual, you probably don't have a loan on that specific piece of gear (but you may have a credit card bill for other gear) and you won't be equating floor space in your house as costing you money (it is, you are paying to run your house). The costs are hidden and it's not so urgent you clear the space and sell the gea unless you need the space for something else. You also will be emotionally attached to a piece of gear.
It only really becomes an issue when you run out of space at home and need to declutter, or the bailifs come round...