It wasn’t the planes that caused them to fall. If that’s the case they would have fell upon impact. It was the fires fuelled by tens of thousands of gallons of jet fuel, which weakened the construction of the building and its ability to hold the higher floors above it. The reason it fell so ‘neatly’ is because of exactly that, they collapsed in to themselves due to being unable to maintain their structure. There was no reason or force upon them to fall any other way.