That term was invented by a communist who spent his adult life telling lies on network television.
There was no "greatest generation". Generational stereotyping is done by idiots.
The name stuck because that was the generation that fought Japan and Germany and others at the same time - and won.
Today our thugs, goons and fools would invite German ‘students’ to study at MIT and accept cash and diamonds for to ‘influence’ people who might offers favors for our enemies. They really were a great generation...