The Bluetooth and Wi-Fi toggles in the Control Center have always allowed users to disable their respective radios since iOS 7. However, this is not the case for iOS 11.
According to security researcher Andrea Barisani and Motherboard, toggling Bluetooth and Wi-Fi off in iOS 11’s Control Center will only disconnect your iOS device from their respective accessories. Barisani told Motherboard that this new interface is not ‘obvious at all’ and makes the user experience more ‘uncomfortable’. If the user unknowingly keeps the Bluetooth or Wi-Fi connection on, it increases the exposure to potential attacks to the hardware, firmware, and software of the device.
While you might think that this is a software bug, it isn’t. In fact, Apple deliberately designed them to function this way. According to its support documents, both Bluetooth and Wi-Fi will continue to be available so that you can use important features such as AirDrop, AirPlay, Apple Pencil, Apple Watch, Handoff, and Instant Hotspot. If you want to disable Bluetooth or Wi-Fi completely, you have to go to Settings to do so. Even if you have done so, both Bluetooth and Wi-Fi will be enabled automatically at 5AM the following morning.