[yvanleterrible]

To answer the OP... Aside from the three first posters' responses which are right, and a reason to pay for icloud that someone else mentioned, I would add piracy deterrence. If you examine iOS ecology closely you'll find that many rules of engagement are meant to slow down file exchange and right down prevent it. What happens when you plug an iOS device on another computer? What happens when you try to put a picture on an SD card through the SD adapter? Why are wifi storage and other computing devices not seen from the device itself without help from other third party apps? Why is printing control so difficult and crude? ...Apple does not want you to give away data with their consent. It is partly about piracy but mostly as a measure for protecting their media sales...