Big O happened because DC wouldn't allow Japan to give Batman a giant robot.
Modern Sentai happened because Marvel was totally ok with Japan giving Spiderman a giant robot.
The moral here is Giant Robots are great.
@djr well, it's not a direct line, but it's still there. When Spiderman was adapted to Japan as a Toku show, the writers basically went "Oh Peter is a genius what if we gave him a giant robot?" This predated even Super Sentai doing the giant robot trope (not until battle fever J did the rangers have a giant robot)