Good points about the elderly as willing or unwitting mules.
I am not willing to credit TSA or HS with the same logical thought process though. The searches are largely politically correct quota policies to appease the ACLU and CAIR and their ilk.
The good news is, even in their ineptitude, there’s a possible unintended upside. While racking up their required numbers of non-muslim/middle-eastern-looking subjects, they may just accidently stumble upon an actual threat of the scenario you describe. Of course, they’d be unprepared for what to do after the discovery. (”Wait here while I call my supervisor...”)
Actually, you should credit the DHS for this as it originated from existing intelligence on airline threats.
The fact that it fits with the PC crowd just illustrates how widespread a threat we face.