Originally Posted by
CDKing
Its because you are obviously a threat to something if you are not traveling with someone else.
I still remember the first time i experience chat-down at BOS. I was being treated as a criminal. Once they found out the woman being interrogated by the other BDO was my travel companion they lightened up. They scolded me for not telling them i was not traveling alone

This was the CPB according to the OP, not TSA.