They designed the buildings to implode because on the 60s and 70s there was a worry that buildings would topple over onto neighbouring buildings if damaged or compromised, and was a legitimate concern as architects were putting forth designs using less reinforcement because they didn’t need as much half a century earlier to build things like the empire state building thanks to better building techniques and materials.

They did exactly what they were designed to do when their integrity was compromised to the point to failure, which is impressive feet. Just ask any engineer what happens when a small but dense and fast moving object slams into the end of a second class lever.