I wish they'd ifx this too. It's so aggrevating :[
Apologize for the frustration. I am checking with the team to see if this is a bug in Adobe Animate.
We have talked about this for years. It's more of a fact of life than a bug, and in some respects it's a good thing. The icon you need for iOS is often different to the one you need for Android, and to have ADT go through your icon list and ignore some icons of the same sizes as Android needs, because those ones are for iOS, might be too tricky.
The app-descriptor could have two icon sections, one within iPhone and one within android, but again that's more to have to maintain.
As there are other things that are Android specific, and even Android store specific, these days I have a different shell FLA for each store, and so each one has its own app-descriptor file.
BTW, my earlier work around to the issue, when I was frequently publishing the same FLA to iOS and Android, was to have a text file that had my list of icons in it. I would then manually copy the list into the single app-descriptor file.