There are just many experts that say it was not an inside job as there those that say it wasn't. Those who say it couldn't happen by happenstance the way it went are usually men of good intentions with just enough intelligence to let them believe so.
However, many of the people who say it was no planed inside job are by a gathering of many great minds, one whom experimented and came to same conclusions; it was attack and the buildings fell the way they did cause when they built they could never have fathomed such great heat in such a short amount of time.
I won't go any further, as this matter has been discussed over and over again to being very boring. Bottom line, there will always be differing theories just as with JFK assassination. We may never know all of the facts. I'm sure there are some hidden facts, just as there is with the JFK case do to intelligence needed to be kept from us.
**************** Progressiveness Must Die Today, In Order That We May Be Free Tomorrow