The Apple Vision Pro integrates with iOS which is something the Quest will never be able to do. That's potentially worth the extra $3000 since there's no other way to do those things if you want to do those things.
It's more of a business issue than a technical one.
what things?
Of course, there's the issue of actually getting them, since the Quest store is different from the usual Google Play store.
However, on iOS, I bet the app store policies wouldn't allow it.