I think building 7’s collapse was a preventative failsafe collapse to keep presumed enemies from gaining vital secrets should New York had suffered some sort of Nuke or other devastating attack....like the Trade Center bombing. One copy of our Constitution in DC for example is supposed to drop down a special shoot in DC incase of attack for protection. I think it was something simple as that.
It takes professional demolition companies WEEKS to prep a building that size to be taken down.