I believe it's just too easy for people to walk into a building, drop a bag off and say "Yeah, there is a bomb in it".
RPly people have to react to it immediately. Calling in a state of emergency, police, evacuation and so on. There 100% are people, who can provide some solid and good RP with bomb threats, no doubt about it. With that being said though, the ability to just walk into a place, pretending to have a bomb just to leave the area afterwards and not continuing with further RP just becomes stale after some time.
I maybe just had some bad experiences, just wanted to bring some attention to it. I definitely agree with the points mentioned above though from an LEO perspective mentioned by Squirtle.