Yeah, because a savage who's made up his mind that he's going to commit suicide and take a couple or a few score of innocent people out with him is probably the kind of person who'd have second thoughts knowing he stood a 1 in 1,000,000 chance of having his back-pack inspected by a cop.
Sheesh.
Look, you have a cop(s) there the bad guy has to pass the cop. He has to not get searched or tip his hand as he walks by the cop. He's on the platform, he has to not tip his hand to other people who might summon the cop. It makes perfect sense.
Also, I have something of a vested interest here, since I'm betting my life on these measures.