It's a shame that the Joint Chiefs of Staff Chairman, Lyman Lemnitzer is no longer with us. He could probably give you the answer himself seeing as he had a similar plan. http://en.wikipedia.org/wiki/Operation_Northwoods
why did "the government" need hijacked airliners if "they" already had the twin towers and WTC7 wired for controlled demo?
My personal opinion is that the event was made to be as spectacular as possible, and that there was some kind of money deal on the side, behind the demolitions, since the towers needed so much work. The hijackers were patsies. Yes, they wanted to crash into buildings, so they got their opportunity...with a little help.