My younger brother joined the Marines and I asked him his reasons and his (anecdotal) reason ranked as
1. I had no purpose in life
2. I didn't care for the people in my life
3. I had no future in life
4. You (kiaman) would understand his wanting to find himself
It's pretty much what happens during times of crisis and war. In peacetime, if you get a couple beers into someone who is serving (or recently served), they will confess they joined for their own purposes and reasons (economic, for personal excitement or adventure, for the structure, because it was better than jail, the prestige of having it on their resume, a career path to something, GI Bill). But during wartime, all of a sudden everyone be like "I joined to protect YOU, I'm the sheepdog, and all the sheep have me to thank for freedom. I could have done a lot of other things for more money and didn't risk my life."
When you give someone a risk-free choice of narrative, are just handing them the golden opportunity to claim superiority of motive or reason without any fear of skeptical rebuke or doubt, it's a rare bird who won't take it.