So since the protocol contains basically no authentication other than the MAC address of the keyboard which the attacker can easily figure out, why isn't there

So since the protocol contains basically no authentication other than the MAC address of the keyboard which the attacker can easily figure out, why isn't there already a key injection portion of this exploit ala wireless USBdriveby? I can totally see this being extended to wireless keyboard and mouse combos which would give you a great way to know if the user was at the computer and when it would be safe to compromise it without someone noticing.