My number may be off by a percentage point or two, but I heard a 3-star brief it, and I've read it in print. It goes something like this:
Of the recruiting age pool of talent (18-25 year olds), appx 72% of them will be found to be immediately unqualified and unwaiverable for military service due to a myriad of things:
academic performance
failure to meet acceptable physical standards
criminal record
medical problems
habitual drug use
personal beliefs (racist, etc)
tattoos (inappropriate subject / too many / too large / too visible in uniform)
other disfigurements (self-inflicted scarring / piercing)
Certain medications (like Ritalin) used beyond a specific age
other issues
Of the list, only the first two really have a remote chance of being corrected, and only if the individual has the motivation to do it.
So, the pool of talent is automatically down to only about 28% of the potential population. Then you can take away all those people who have no desire whatsoever to be in the military, for whatever reason. This removes from consideration many of the privileged who have more opportunities available to them, as well as some demographics where service is not necessarily viewed favorably. Half of the population (roughly) is female, but the current needs of the services could not handle more than about 20% of the force being female, based on current restrictions (direct combat infantry, SEALS, Submariners, etc). This percentage will probably continue to change over time.
Now you've got four services vying for the same limited number of qualified recruits. That's why every year you see all sorts of signing bonuses, changes in the max age they will accept an initial enlistment, etc. My hat's off to the Marines, because their standards do not change very much year to year, and while they don't (to my recollection) offer signing bonuses to an enlisted recruit (like Army does in certain circumstances), they still manage to make their numbers. And, despite evidence to the contrary on this website, their percentage of high school graduates (an indicator of the intelligence of their work force) is higher than the other services. It doesn't hurt that Marine Corps Recruit Duty, I&I duty with the Reserves, and Instructor duty (ROTC, etc) are all viewed favorably from a career management perspective, and it is recognized that front runners need to be placed in those critical entry points.
A successful recruiter works his / her tail off, and invests a lot of time in a prospect that may or may not pan out.
No one is accusing anyone of a "recruiting scandal" in this case although those have occurred in the past and will occur again. But Command, whether tactical or administrative, demands results. You will be held accountable for the ability to complete the mission, whether it is putting bombs on target or getting qualified recruits on the bus to Great Lakes. Most who aspire to Command understand the responsibility, welcome the challenge, and would not have it any other way. It sucks when a good person inherits a can of worms, but that's part of the leadership challenge.