It is not about resolution, but about pixel density, which is 326 ppi, which has been the standard density of all iPhone retina displays since the iPhone 4, except for the plus size models which have 401 ppi screens. Now Apple could have used either LCD fab, 326 ppi or 401 ppi, but note that the plus size models have 16:9 screens, but the iPhone 11 does not. So if Apple wanted the aspect ratio of the iPhone 11 (XR) but went with the 401 ppi fab, then the screen would still have an awkward resolution (I don't know if it would be higher than 1080P and if video has to be scaled up in that case, which could be worse). Also consider that the 326 ppi fab could have better high volume production yields than the 401 ppi screens (and the 401 ppi screen could not be delivered in the quantities Apple needs).