Increasingly phones are being obsoleted by software and not the hardware which is still technically capable of running n+7 yearly OS. 10 years would be a good target for software support.
To be fair, a nicer, more expensive, more reliable windows laptop would also have been an option.
Though I guess if they did like Google and updated a lot of OS components through the App Store (which I agree they should) then you could have security updates for most stuff without major UI updates that slow you down, that would be cool.