Why isn't new InstantiatePrefab API covered by the auto-update wizard?

Lots of people come to ask why the new 2018.3+ breaks some old script. It's happened to my old scripts too. After some googling and reading the docs I fixed the one line necessary.

Typically, when APIs have changed and broken old code, a wizard pops up on file import (or even post-edit re-import) and does a fairly decent job of fixing the code to use the equivalent new approach.

Why wasn't this added to the updater wizard on day 1 of 2018.3?

 

Here is the InstantiatePrefab method in 2018.2:
https://docs.unity3d.com/2018.2/Documentation/ScriptReference/PrefabUtility.InstantiatePrefab.html
And here it is in 2018.3:
https://docs.unity3d.com/2018.3/Documentation/ScriptReference/PrefabUtility.InstantiatePrefab.html

As far as I can see, there is no upgrade required here. It must have been something else breaking your scripts.