Well, lets look at this all more simply:
Planes only became useful for anything like an attack, right before WW1. The first time they were used directly with the idea of the pilots sacrificing themselves as a guided strategy, occurred during WW2, a short thirty years later. From the end of WW2 to now, none of the people guiding the many wars that were fought, thought to attack the American homeland directly. Why, I don’t know, I would attribute it to the same reason why we never worked to defend against it in advance: failure of imagination.
Chance, in a way. Lots of very positive things and inventions, have also been right in front of us for years, decades, centuries, even millennia, before the right person with the right resources and allies finally acted.
Did you know, that steam engines were invented in ancient Greece? But no one thought to use them to create motorized ships or land transports, until over two thousand years later.