Thank god that you can't plug in an SD card into an iPhone. Disallowing that was one of the smartest decisions by Apple.
In Android world there's the constant flow of "why can't I save the app, or app data, or why doesn't the app save the data onto the SD card, and keeps dumping everything into internal storage".
If that expansion worked reliably, consistently and in non-confusing manner. If apps could be reliably, consistently and in non-confusing manner bet told to install to external storage, keep their data there, and save their data there.
In Android world there's the constant flow of "why can't I save the app, or app data, or why doesn't the app save the data onto the SD card, and keeps dumping everything into internal storage".