> the software makes the hardware unusable or insecure because of the lack of updates pretty quickly.

Or, alternatively, the (practically) mandatory updates make the previously perfectly fine phone slow to the point of being unusable.

I'm saying that the updates are practically mandatory because if you don't apply them, your apps gradually stop working (as they cannot talk to their respective server backends, which are being updated without maintaining backcompat) - and of course, the current version of the app requires the current(ish) version of iOS. This all amounts to an engineered obsolescence of millions of perfectly good phones.