[lmm]

Low trade-in value is a reason a lot of those devices end up as hand-me-downs; there's no liquid market so they're notionally worthless, but they still work so people are likely to pass them on rather than trade them in. (Indeed one could argue that Apple pays inflated trade-in values to get their old models out of circulation and sustain their premium positioning)

[GeekyBear]

One could argue that Android vendors intentionally refuse to support low end Android devices after the sale to force users to buy another device every year.

[lmm]

One could, but the competitiveness of low-end Android makes that pretty implausible; people buying a cheap no-name Android who replace it with another cheap no-name Android are unlikely to get that from the same company.

[GeekyBear]

It's not implausible at all. It's an intentional choice to refuse to provide support for low end devices, seen across the board.

[lmm]

It's implausible that it would be for market control purposes, because no one player controls that market and competition is intense (unlike Apple's situation). If no-one's offering support in the low end it's because doing so is uneconomic in itself, not to create an effect in another part of the ecosystem.