Apple blocks downgrading to an older iOS version
Apple has stopped letting users degrade to an older version of iOS from the latest version.
Bad news for Apple users! If you have upgraded to the latest iOS 11 and aren’t satisfied by new features or being bothered by bugs, then you can no longer go back to the previous version of iOS. As reported by Softpedia, Apple has blocked downgrading from iOS 11 to iOS 10.
The latest iOS 11, like every new software release, came with its own set of bugs and Apple has been releasing subsequent patches to iron them out. Previously, iOS users had the option to either wait for the next patch or go back to the previous version of iOS. Now, users will have to wait for the latest iOS 11 patches if they are being bothered by a specific bug.
Apple hasn’t stated any major reason for this decision but it seems that company doesn’t want its supported devices to go back to an older software and become vulnerable to security threats, despite iOS being a more secure platform than that of Google’s Android.
(source)