It should be based on the app size, so maybe developers will stop shipping apps with a single feature and one button that takes 700 MB because of random bloated third-party SDKs that aren't even used.
They need locale-based app bundles to make that realistic then. If I need to support every locale I can, I need to bundle the frameworks necessary.
Money makers on the AppStore are games, and games need assets in high definition. Third party SDKs are probably a drop in the bucket in comparison with visual assets.