Because nobody could ever hook up an ARM SBC to the LVDS connector on a 17" laptop and play a video to fake a boot sequence that would fool a telemarketer in purple gloves, leaving the rest of the case available for whatever can be molded into plastic.
Because TSA is there to protect us from imbicilic terrorists, even though 9/11 was orchestrated by degreed engineers, physicians, etc.?
Or just maybe it's not about terrorists but rather obedience conditioning, and they need a new rule once in a while to keep the people regressing (from presumption of Constitutional rights).
Only one of those hypotheses fits the data.