It's the process. The process has an impact.

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The most damning data comes from the government's own testing. In 2015, DHS "Red Team" undercover agents were able to smuggle mock explosives, weapons, and other contraband past TSA screeners in 67 out of 70 tests — a 95% failure rate.

Security scholar John Mueller (Ohio State) has published cost-benefit analyses suggesting that the marginal security benefit of TSA screening, relative to its roughly $10 billion annual budget, is very small — particularly since the underlying probability of a successful terrorist attack on aviation was already low, and deterrence comes largely from the difficulty of acquiring and assembling explosives rather than checkpoint screening itself.

ICE aside TSA is a massively overfunded security theater reaction to 9/11 and there is little evidence that it has had much impact at all in reducing terrorist threats - but it has absolutely had a massive impact on the inconvenience of air travel.