And I really don't understand it. Those apps would be perfect example apps for developers... they use a variety of frameworks and are not overly complex.Always used to be a thing that Apple would always make a universal app, partly to set best practice for developers to follow.
For some reason they stopped caring about that a few years back. Look at Journal for example, if that had been released a decade ago it would be on all platforms from day one. Yet it was iPhone only for 2 years.
I remember when Mac OS X 10.0 came out, Apple still followed the NeXT example and included the source code of TextEdit, MailViewer, Stickies, Chess and some other stuff.