Every major operating system development company has had to face the issue of abandoning legacy versions (and former customers) in favor of gaining market share and utilizing technologies which were formerly unavailable. Microsoft did it when it the end-of-life of Windows XP in April 2014. And so it goes with Apple and iOS8.
But Apple's market dominance is so huge that older products are now sold in third-world countries where Apple Corporation doesn't receive one dollar of the sale. The secondary market has developed because the technology is robust and worthy of continuing support.
There’s more than one reason why iOS 8’s growth has stalled | Ars Technica
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