According to DailyMail they did it for fun, as a joke or something. When the Humvees were hitting the ground the riggers were taped hooting and laughing and yelling things like, 'Hell Yea!'
Just demented kids who have no concept of consequences and were given a job that was too big for them. It was a joke of some kind. I can't understand it? They did it just for fun.
I'm glad these guys did not make it to the battlefield. Who knows what they would have done. Dangerous people.