airports where they have agents working in security
This is the most likely scenario. They might be trying the Daallo Flight 159 type attack again. But here's the problem with a laptop ban: If the bad guys have penetrated security to that extent, they can pretty easily plant anything they want onboard an aircraft or hand it to a co-conspirator passenger. Why bother with a laptop when they could hand the guy a complete carry-on bag?
If this is indeed the threat, then we need to shut down flights originating from the compromised airports completely. And then work with the local officials to plug security holes.