"The fact iPhones are well made and continue to chug along so well brings along an ancillary benefit: they retain their value much better than Androids. Which, again, makes them attractive to buyers in the second-hand market. Apple sees nothing from second-hand trade."
It is a total fallacy that this is costing Apple lots of money.
New iPhones are so expensive that only a niche market can actually afford them, even considering operator tarrifs which include a premium that pays for the handset over time. The fact that those lucky few have a market to sell on the older handsets is of benefit to Apple because it provides an upgrade path for its existing customers and also goes a long way in promoting its brand.