I am not sure we have the evidence to say that.
The nation our grandparents lived in had literally been attacked, bombed, and torpedoed by armed forces of Imperial Japan and Nazi Germany. Those two nations pre-emptiveily declared war on us, and our nation's well-being and perhaps survival were at stake. Everyone in 1941 knew that Japan was bent on dominating Asia, and that Nazi Germany had the ways and means to subjugate Eurasia with direct consequences for the well being on people in North America.
Those are profound and existential reasons for people to be motivated and prepared to fight.
Sending a kid to kill some Vietnamese in a jungle in southeast Asia in a civil war that is no significant threat to our country - or sending American kids on false pretenses to invade an Arabic country that poses no substantial threat to us are not exactly the types of existential threats that make people feel morally obligated and motivated to fight for.
If our generation of kids every had to face the kind of threat that Nazi Germany and Imperial Japan represented to the welfare and safety of the citizens of our nation, we simply cannot speculate how they would respond. They might well respond in ways that are just as admirable as the "greatest" generation.
We really can. Take a look around. It is not getting better. I respect your opinion though and applaud your optimism.