In Apple's case; I don't think malice is why they do what they do, it's probably a byproduct of a much simpler reason. As posted above, security might be one. If a device is harder to take apart, it's also harder to tamper with. I personally think that this would only hold up to some degree as an attacker with enough resources could get in anyway, but perhaps the required resources are are a high enough level that common attacks are less feasible.

Another thing that is a way bigger issue (in my hacker mindset) is when SMT/SMD became common, just like VLSI. You suddenly can no longer easily see how a circuit works, and repairing a few failed components on a PCB gets much harder for most people. Then again, the cost (in time or paid time) is also no longer reasonably to have someone else do it. Replacing hardware and the benefits that can come with that are often a better deal than a repair.