secured income. wish to adventure and see other places. To avoid the normal life. Life for most during those times wasnt nice or easy. If you were a peasant,that meant manual labour from sunrise to sundown each and everyday, with not so great diet. For a young man military career was an viable option to make a living,specially if he was a one of the younger children,that the parents couldnt have left anykind of inheritance,since it would have gone to the oldest male child.
From army you would get a place to sleep,food and clothes and also small pension as you retired.All that a normal man would have wanted those days. Ofcourse there was risk to die,but there were plenty of risks for dying those days,even without gepardizing oneself intentionally.