But really, what you're complaining about is CYA (cover your ass) security. It's a lot easier for the person in charge to decide to clear out the building, and answer to a bit of grumbling with "just doing my job to keep you people safe" than it is to deal with the (extremely unlikely) fallout that would come from ignoring a real bomb.
I mean, that is the Essenes of a bomb scare as opposed to a bomb threat or an actual bomb, no?
Pitt has the tallest educational building in the US (Cathedral of Learning - which has had 14 bomb threats), plus many other buildings on campus are rather tall too. I cannot begin to imagine how exhausting these bomb threats have been to the police. Many people don't want to evacuate the buildings either. But what if some lunatic takes advantage of how desensitized and relax people are becoming to go a shooting spree... that is the more scary thought.
And today is the anniversary of the 1995 Oklahoma city bombing.
However I am uncertain if a "threat" was ever called in for either.
This is evidence that a called in thread will likely never be real - real attacks aren't called in with warnings.
The unibomber is one example. He would send mail bombs if newspapers didn't heed his threats and publish his ramblings.