It's the same as the TSA - they're not very good at catching people bringing things through at airports, but their mere presence there acts as a pretty good deterrent for people trying funky things.
To put things in perspective, the various federal and state welfare agencies in Australia employ something like 200K bureaucrats to allocate and monitor welfare handouts.
If they were all made redundant, the money saved would add a significant amount to the available welfare budget.
I worked as a consultant at several of these agencies and I can assure you that most of the jobs there were bullshit.
One coworker described these places as “daycare for adults”.
(The UK has a particularly extreme version of this: the benefits department is hellbent on rejecting as many applicants as possible, and they lose a huge amount of court cases because of it, at great cost to the taxpayer and the lives of those affected)