Terrorism is an infinitesimally small threat, but many on the political side chose to treat it with heavy gloves despite the diminishing returns because (1) the Zero-risk cognitive bias makes people want to force than small risk to zero [1] and (2) the federal government views the TSA as a jobs program. Even though they're largely ineffective, no politician would dare to propose the dismantling thereof because the opposing side could use this as ammunition in the form of 'X is allowing the terrorists in' or 'X has cost us 10,000 jobs.'
Terrorism is an infinitesimally small threat, but many on the political side chose to treat it with heavy gloves despite the diminishing returns because (1) the Zero-risk cognitive bias makes people want to force than small risk to zero [1] and (2) the federal government views the TSA as a jobs program. Even though they're largely ineffective, no politician would dare to propose the dismantling thereof because the opposing side could use this as ammunition in the form of 'X is allowing the terrorists in' or 'X has cost us 10,000 jobs.'
[1] https://en.wikipedia.org/wiki/Zero-risk_bias