One issue is that security theater creates demand for itself. Do things that induce worry and a tendency towards paranoia in the more susceptible parts of the population and then you will gradually raise the general alertness of the population. This then manufactures a desire for these measures. It largely rides off of people's general unwillingness to entertain just how many of the measures are ineffective or nonsensical. "It can't all be pointless. Surely some of it must make us safer." It's not an unreasonable belief in itself, but everyone having that attitude lets security theater grow cancerously.