If it was security as claimed the laptops would not be allowed in checked luggage either.
Depends if there is extra screening before its checked. There was a theory amongst reddit commentators it was so some 3 letter agency can install tracking chips. If we are going to dabble in speculation we may as dabble in all of it.
So you are suggesting the the US are deploying agents at airports in foreign countries? That sounds very unlikely and very hostile.
I disagree for a very simple reason: Screening is not being carried out properly.