Because it was right in the debris field of the buildings..and there was significant damage to buildings all around the area, windows were blown out for blocks, cars were overturned..
Remember the NYC emergency operations center was housed in WTC on 9/11 there was emergency backup fuel stored in the building to run generators in case of emergency that exploded and caused significant fires to break out....
Where I live, a 20-story build was brought down by a controlled demolition and it blew out windows 4-5 blocks away, just imagine what a falling 100 story would do
Why did no other buildings hit with debris fall? Why only WTC 7?