according to the reading, why did the towers at the world trade center collapse?

The towers at the World Trade Center collapsed primarily because of the intense fires that followed the impact of the airplanes. The airplanes caused significant damage to the structural components and dislodged the fireproofing insulation. This allowed the fires, fueled by jet fuel and the buildings' contents, to heat the steel columns and floor trusses to critical temperatures, weakening their structural integrity. The weakened core and perimeter columns eventually buckled under the load, leading to a progressive collapse of the towers. The prolonged heating caused the steel to lose its load-carrying capacity, and the floors pulling on the perimeter columns caused them to buckle inward, collapsing the entire structure from top to bottom.