What RF protocol do wireless mouses and keyboards use to communicate?
I believe that the wireless mice and keyboards only transmit when an event happens, while BLE has an ongoing "pairing" traffic. TX-on-demand moves the power consumption to the reciever (which is not on battery) but it makes it impossible to tell when the keyboard has gone out of range.

They're also single-direction (apart from keyboard LEDs, which may not be present), while BLE can exchange data in both directions.