Because announcing it as a drill is less threatening to a person than the real thing. It's like having a fire drill in your school....the authorities in the school take it serious as a real one but the people not involved in the organization don't take it seriously.
You announce a fire drill in a school, there's no real fire. The principal doesn't announce it over the PA, then start a bunch of fires in the hallway.
People not involved in the organization took it serious Monday when those bombs went off.
No one went, "It's only a drill" when it happened.
There's several possibilities, but in my opinion, it would be done to alleviate anxiety in the face of a heightened presence or a lot of security personnel.
I doubt people felt that alleviated anxiety when two bombs went off and people had limbs blown off.
Seeing a bunch of security does nothing to help the fact that two bombs just went off near me, I have no idea what's happening, I'm running as fast as I can away not knowing if something bigger is coming. Seeing a bunch of cops/Craft guys/other private contractors running to the area doesn't make me calm in that situation.
And I think I posted it in this thread, if not one of the other related threads.
The Boston Marathon is the biggest event in New England. 2nd biggest media event behind the Superbowl in the world. They get about 25k runners and 500k spectators each year. I was actually talking to someone from Boston that flew into Chicago yesterday and he was talking about it, he said they call that day Marathon Monday. Almost everything in the city is shut down and tons of people just head down at some point to watch it. His wife was a couple of blocks away from the bombing and he usually attends but didn't this year. But, the marathon is a big deal, a ridiculous amount of people are there every year.
From an 09 posting
http://www.urbandictionary.com/define.php?term=Marathon Monday
Marathon Monday is often considered, among Bostonians, as the greatest day of each year. Falling on the third Monday of April, the marathon provides a race as a backdrop to the biggest day of drinking and legalized hookie-playing found anywhere in the country.
Over at BC the day takes on even more epic proportions, where all classes are cancelled as the race runs right past campus making it impossible for teachers and commuter students to get there. It's basically just a huge excuse to get wasted…really wasted…like blackout by 11:00 AM wasted. The stringent community and campus official restrictions on drinking are relaxed for the day and an anything goes mentality pervades. In short it’s a total shyt show and every college student’s dream.
So you've got a major city shutting down damn near for one of the biggest sporting events in the world, more than half a million people congregating to a 26.2 mile area and a bunch of people getting shytfaced, you don't need an excuse to have a ton of security present. You don't need to announce the drill to make people accept there being a lot of security.