Apple wants to control your device because if you have too much control, you could create a situation that makes you, a government, Apple as a business, application developers, or other users feel that Apple did something wrong.

Whenever there is a centralized entity with the power to change things, people will eventually treat it as though it is responsible to change them. This is why we need decentralized systems. Freedom, choice, and efficiency for users comes from using decentralized systems — like the web + browsers.

I don't think the argument is good enough to justify their behavior. But it is why they do it.