Most of people know about wars from TV, newspapers, internet, video games... The bad thing is that they never pay enough attention to those, who were fighting for possibility of others to know about war only from media.
Not every homeless former military member served in a theater of operations (a war), several just like civilian homeless just made bad decisions. Service in a operational theater is not an excuse to be homeless
The problem PF is when a member of the reserves leaves the military to go on EI (something that happens a lot on the east coast) no one keeps track of where they go. Since the CF is then no longer playing parent (you can join the reserves when you are 17 so it is conceivable that these kids have never really lived away from home) they party it up. So after they drink, gamble or otherwise blow through their cash they are flat broke, then when the EI payments stop they either join back up or try and find a job some place else. Sometimes they never get another job and end up living on the streets. Im sure that there may be some out there who are mentally ill, and just dont seek treatment, and end up living on the streets because they are unemployable. However they are the exception not the rule.
Everyone should be doing more to help.