The difference between horror and suspense is that in horror, two people meet at a restaurant for lunch, and then a nuclear bomb will go off. In suspense, you'll see the bomb before they get to the restaurant.
Terrorism is kind of the same thing. When the goal is to destroy something, you destroy something: you take out manufacturing or energy sources, or military assets. When the point is to demoralize, you show them somehting. Or hint that there's something.
to go too far into it: take 9/11 as an example. The intent was not to hurt, but to scare. As many deaths as there were, it was not a significant portion of the US population. As important as the WTC was, it was not going to economically hamper the US's ability to respond or act (at least, it directly wouldn't). The point was NOT to take out assets, but to scare the government and citizens by showing them what could be done.
That's why you call in a bomb scare. TO make people realize they're vulnerable. Not to actually kill them, although that's sometimes the result. Alternatively, it's to make a demand, for ransom or something. there has to be a threat before there can be a demand.
Another reason to call in a bomb scare is to get out of class for the day, which, when the bomb scare is at a High School, I suspect is more generally the case.
