I don't see why the battery would matter, unless you are forced to use power saving performance throttling. Flash memory degradation may be a factor, as well a

I don't see why the battery would matter, unless you are forced to use power saving performance throttling. Flash memory degradation may be a factor, as well as increased expectations. Also, the perceived value of the product doesn't increase much if the device lasts longer than some average lifespan. For smartphones I believe after 1-2 years most users move onto a newer device, any cost that increases the life of the device past this point is wasted and will result in a more expensive, less competitive product, so market forces push for decisions that may be perceived as planed obsolescence.