My iPhoto photo set is much, much larger than Google Photos storage cap; I just want to share a couple of photos with family. But yeah, that sort of explains it. They're pushing you to just store everything in Google Photos.

The issue is you have an existing photo in your iCloud that is not in your camera roll (which is something iOS can automatically do so many people have this use case) there was no easy way to transfer those photos to Google.

This is something I miss from Android. I could tell Google Photos to ignore my downloads and screenshots albums, but iOS you either need to manually select photos to upload, or upload all photos.