This is because Apple uses a common ID and password across all its devices, iPhone, iPad, etc. But things can get pretty awful pretty fast if you forget the Apple ID or password. It's not a big deal if you forget a password or ID for some inactive account somewhere. With the great proliferation of passwords and IDs on the internet, one can be forgiven for sometimes forgetting crucial IDs and passwords. You might also require this when you have forgotten the Apple ID credentials for no reason. When buying a second-hand iPhone or using a disabled device, this situation arises. Do you have an iOS device but no access to an Apple ID? In such circumstances, you might have perceived it is impossible to reset iPhone without Apple ID.
