Usually I don't talk about it not because it's hard to talk about, but because other people don't understand and they like to judge.
There's a lot of truth in what you wrote, I find this to be the truest of it all.
As hard as we try to explain our reasoning, some will just never understand and that is perhaps the most frustrating thing I have ever experienced in my life. I gave up trying to reason with people a long time ago, my explanations fall upon deaf and indifferent ears.
The answer is "simple", everyone has a different reason.
Some do it for the thrill, some for the sense of purpose, yet others do it because they need a way out of the life they were living back home. Todays military is a complexity that few can ever understand without living it.
Me? I come from a long lineage of service, something that I am particularly proud of. A family tradition of public service and giving back to my community, something I was taught from a young age to appreciate. That was my driving force and to this day it still is in everything I try to accomplish in life.