Simple: they are a complex piece of technology. The photo above shows a Macbook charger from Apple on the left: the charger on the right is from another company. You can clearly see that the one from Apple has a lot more technology packed in there. And for good reasons. To understand what those reasons are, see this piece: Macbook charger teardown: The surprising complexity inside Apple’s power adapter. It was surprisingly interesting, from an engineering and design perspective.
Thanks to Tom Plaskon for sharing this on Twitter!