No, its not optimized for cost. Manufacturing is optimized for _profit_.

>they don’t do that to make it harder to repair

you mean cryptographically linking lcd screen to motherboard is done for cost, not to stop third parties from being able to repair it?

It's done for security because the screens are primary input devices and linked to the biometric sensors. Without protections for genuine components anyone could replace your screen with one that had a hardware key logger and compromised biometric sensors. The security of the system is as weak as the weakest component.

Your phone has access to tons of personal data, for some people just about all of their personal data. It's in every user's best interest to have secure hardware since it's inherently mobile and easily lost or stolen, easier than a desktop locked in a house.

But no I'm sure it's just some conspiracy to make iPhones disposable. That makes way more sense.

It can be for both reasons at the same time, Apple is absolutely massively incentivized to make 3rd party repairs impossible.

not just electronics, John Deer tractors and farming machines... all the parts have encrypted links that only John Deer repair shops can sync new parts... soon your car won't let you change your tire without it not turning on, unless you buy their "tire"