People are dumb. The principle is that devices help us all get round that. Users are not perfect, we all err. If the designers had thought ahead, or may be back, like Aslan the lion, that part is uncertain, they would remember that people are dumb, and make safety features to stop people doing dumb stuff.
Safety features included with an iPhone are as follows:
1. The option to passcode lock it.
2. The option to automatically back up precious data to iCloud.
3. The option to activate an iCloud activation lock to prevent thieves from using your phone.
4. The ability to locate your phone.
5. All sorts of accessibility features.
6. The ability to re-download music, apps and video you previously purchased without having to re-purchases them in case you accidentally delete them.
7. Other stuff
That is providing more than enough to protect people from themselves, but no matter how you slice it, the purchaser is ultimately responsible for the things they buy, and you know it.