Notice how they always seem to recruit in less privileged towns and areas. They also tell you of all the places you'll travel, all the skills you'll learn, all the experiences you'll have... but they always seem to forget to tell you that the main purpose of the job is very frequently to kill (or threaten to kill) people and to have a very good chance of being killed yourself.
I agree that, for many, it isn't a completely freewill choice whereby they've considered all of the many and varied exciting options available to them and actively chosen that one; more that they don't have any other exciting options open to them so they think they've got nothing to lose.