Personally, iMessage and shared iPhoto galleries between a dozen family members around the globe make it fairly "sticky" with me, but there's no reason I couldn't just consume the photos on desktop.
I'm not sure I have much of a point here, but I don't think the switching costs have ever been all that high with mobile, and since the popular platforms are pretty mature, most 'necessary' apps are cross-platform.
Just last night I re-evaluated the various photo services that were of most interest to me (Apple Photos, Google Photos, OneDrive, Amazon Photos), and settled on Apple Photos. As a macOS/Windows/Android user, who is normally pretty aggressively platform-agnostic I see abandoning mobile access to my photo library as the least-bad option available.
Chinese users also buy apps, take photos, watch movies, listen to music, create content. All of which on iOS is tied to the Apple services ecosystem and hence the switching costs are still significant.