I know that in some cases, apparent bloat like this is related to needing to support so many potential devices and versions of the underlying OS. Google has to support, on iOS, roughly 6 years of devices and their variations + OS variations on them. Each of these may require their own libraries compiled against it, for optimal performance or because it simply is less practical to engineer non-breaking updates against new SDK and HW versions in the same codebase without introducing complexity.

Apple, on the other hand, doesn't have to do this. They can integrate at lower levels and even with all else being equal can develop updates with perfect insight on the ecosystem and foresight on things to come.

Somewhat supporting this possible explanation is that, similar to Apple on iOS, Google's apps on android are significantly smaller.