Photographers protest in NY Subway!

[AReality]

Also those high up needs to cover their backside also.
It's better to give a reason "We tried, but could not prevent fully", than "We calculated the risks, the money spent vs risks, and found that it's not feasible to implement that."

 

[AReality]

But Australia did a risk calculation some time back.
They calculated the amount of money wasted if some ministers are assasinated. But found that it's more feasible to employ bodyguards.