In the case of Debian and F-Droid, they do so transparently, often with reproducible builds. The fact that packages are signed by those groups is one of the reasons why they are trusted. I would not consider "signed automatically by Google" to be an improvement in trustworthiness.

In the case of Apple, I agree. It doesn't make sense to use their ecosystem without trusting them fully.

However, in the case of Android / Google Play, right now the developers have the option to choose between APKs and App Bundles. Why take away that choice? If App Bundles are superior, then developers will choose that option freely. (Google Play is already really pushy when recommending to use App Bundles.)