Here is a repair scenario that you forgot:
You buy a phone, and like it. You use it. A lot. Over the course of using it, the usb charging port starts to become intermittent. It's a part whose value is $.50 or less, but if it can't be repaired, you have to throw the whole phone away. What a waste of money!
The battery in your phone is no longer holding a useful amount of energy to power the phone all day. You could replace the battery and bring the whole phone back to "like-new" condition, but the manufacturer has glued the case together. This is the malicious intent: The manufacturer *KNEW* that the battery would not last forever, and still welded the case shut. You would not stand for this if it were your car.