(I'm aware this is partly cultural desensitization, I remember the memes back when of people looking like shrimps staring at their phones etc).
So far nothing could replace it (headsets, watches, other wearable) because while different ways of interaction exist, the users always needed a screen for (media) consumption.
An AR device could suddenly tick all boxes, make a user buy such glasses as companion device and slowly transition away from his iPhone. So Apple needs to prepare and expand its ecosystem stickyness to AR.
Not saying it's a good bet for Apple or for users, but it seems that's the bet they are making.
That's absolutely obvious. What people are arguing is that this is a terrible move for many reasons. 0.1% of iphone users have a Vision Pro and Apple just degraded the experience for all of us.
They do this because there might soon be a disruptive AR-product (e.g. some nextgen Meta RayBan's) which gets adopted as companion device by the iPhone userbase and then gradually shifts their usage away from the iPhone to that other product.
So Apple needs to expand their ecosystem with all its stickyness to AR, as this ensures that even if competing AR products will be more appealing, they will all be inferior because only Apple's AR-product will allow you to mirror your whole iOS experience with all apps and content.