There were reports that came out that nano thermite particles were present in the rubble of the Twin towers. There are also videos of molten steel flowing out of openings of the towers while they were still standing. I'd imagine with the size of those towers, to get a controlled collapse, they'd have to melt a shit ton of metal, like literally a ton of molten metal. Imagine all that flowing to the base of the towers, and all the rubble collapsing on top. It would basically form a giant oven or kiln and trap the heat for a long time.