Because Apple are one of the gatekeepers now, that's why they're getting regulated everywhere. It's not like how you can move from a Ford to a Honda, a lot of people have their entire digital lives with notes, chats, photos, videos and thousands of dollars of purchases tied to Apple's account, plus the network effect where the whole family has iPhone because of iMessage. Moving to another phone brands, they'd loose all that.

That's Apple's moat and they're fighting to the death for it because they don't have any other cash cow to milk.

Non Apple user btw.