Well, if you join the service you might have to go fight and die for your country. And you might be captured and beheaded on national TV. I'd say that would explain the downturn in recruitment.
And it doesn't help much at all when the military leadership court-martials guys for firing "too many rounds" at the enemy. Who the heck wants to operate under the rules of engagement of a New Jersey state trooper thousands of miles away in a nation full of primitive savages?
Then why did the Marines exceed their goal?