> Probably mainly smoke and mirrors.

That is because CCTV does not directly decrease crime. Instead, it tries to increase the chance the alleged criminal gets seen, profiled, and caught later on which means the alleged criminal won't be able to commit crime for a while due to jail time.

Mass surveillance and CCTV are notoriously bad at avoiding crime or terrorism from happening on the short term though, and as long as there is incentive to either, they'll remain happening.