From a reader:

Airport security is not about actually stopping terrorists. That’s at best a secondary
concern. The main purpose is to generate the appearance of security,
so that people won’t be nervous about flying.
Personally, I think that underestimates the intelligence of the flying
public. But I’ve noted that bureaucrats don’t think very highly of the
judgment of the common citizen.
Another reason is that bureaucrats are quite sensitive to public
criticism, and highly allergic to lawsuits. Their policy of
meticulously ignoring any conceivable characteristic that might
suggest a greater proclivity to terrorist activity insulates them from
those concerns.