Fun fact: The fire retardant used in high rise structures is rated at max, for 4 hours of burning. It's fire retardant. Not fire proof. Learn the difference.
Oh and show me how many planes have been hit by a fucking plane that big that are still standing today.
If you bend/damage a structural meraber with o say....a plane or falling chunks of a building, it will blow off some of the fire retardant sprays. You only need 1 space to be cleared for the beam to fail.
Also, get fucking real when you think that these buildings are perfect examples of fire resistance. A building that's been around since 85 is going to have a shitload of unapproved and uninspected modifications done to it that compromise fire safety because someone is too lazy to do the job right.