How come Ipad mini 2 is still serviceable but not ipad mini 3?

Serviceable? You question may require expansion or additional clarification.

If by “serviceable” you refer to the device as still being within hardware support by Apple, all models have a support lifespan for both update and hardware (repair) support. As devices age, they will eventually cease to be supported by the manufacturer.

Because Apple continued to sell the 16GB and 32GB configurations of it after stopping for the third generation models.

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