Apple has a long history of automatically uploading (and/or "backing up") all documents and media of its customers to iCloud. Microsoft started doing that with OneDrive and OneDrive backups only recently. That + the work Apple put in locking down its phone from users and attackers alike, basically breaks down like this:

                 | Apple         | Microsoft  |
  ---------------+---------------+------------|
  Users with     | approximately | small but  |
  data in cloud  | everyone      | growing    |
  ---------------+---------------+------------|
  Access to      | denied via    | easily     |
  data on device | cryptography  | available  |
                 | by default    | by default |