Every feature that gives any sort of flexibility to the user is an attack vector for the lazy developer.
A simple one is why is there even a permission to let an app read and write all contents on an SD card instead of only allowing apps to read files that a user specifically chooses from a file picker? Or worse case read and write from your photo library or music library.
Besides that, Apple can’t control the entire worlds cellular and WiFi coverage. Some parts of countries only have 3G, some buildings only have shity WiFi. However, Apple can control how their iPhone’s storage performs by not allowing you to use crappy SD cards and just having you opt for more internal storage.