Why was the engineering of the World Trade Center so poorly designed?

On 9/11 two planes full of Muslims crashed into the world trade center, right? Why is american engineering so poor? I thought the USA had the worlds best engineers because of all the durability against earth quakes in california and stuff like that. Many people praise american engineers, and claim these buildings are built strong enough to withstand airplane attacks. I ate lunch at the top of the world restaurant in the world trade center around 1990 and they even said the towers were designed to withstand the impact of a full size airliner and all jetfuel. So what was the poor design of the towers? Or is american engineering really not as good as they say. Maybe Katrina also proves american engineers are bad at what they do?