Unfortunately, technology moves forward at a 12-18 month cycle. Getting security updates for 3 years after the device is purchased is great by todays standards. Remember, the phone doesn’t stop working... but you don’t get the new developments because it would likely neuter your device.

iPhone 4's never got Siri, for…

An October 2017 date should get you Android N, and Android O, and the security updates for 3 years after that.. That’s not too shabby.

Unlike my Samsung Galaxy Note 10.1 2014 addition that is still running 4.4.