I've probably mentioned in past, that when a Clinton-era presidential commission on the under-representation of Hispanics in the federal public service was conducted, the report noted that something like 85% of Hispanic-Americans (at that time, at least) lived in the states where only 34% of the federal jobs were located**. Now, while people will relocate for work, not every manager has a budget to move a new hire. And some folks are in circumstances where they can't really afford to relocate (try selling your home in Detroit, Vegas or Cleveland to move to NYC, or DC).
I won't make any assumptions about where vets are situated, other than that they are pretty much everywhere. And while you're probably right that the lion's share of federal positions don't necessarily require more qualifications than the military did, one still has to be where the job is. If I was really desperate, I might be willing to take anything, but if I had a spouse and kid in Delaware, and was offered a border guard job in New Mexico or Texas, would I be champing at the bit? I don't know.
That's not meant to be any sort of excuse. I'm just saying that the same way employment equity policies don't easily solve that challenge, veteran's preference doesn't easily solve its challenge either. The reality is that, like it or not, geography poses a barrier to meeting some kinds of employment access objectives. Not insurmountable, and not carte blanche for not trying.
**I will temper that by noting that a great many people do commute "interstate" on a daily basis - Fargo/Moorhead, the two Kansas Cities, the southern tip of lake Michigan, the tri-state area around NYC, etc. - so don't let census head counts distract us from whether a job offer is nearby or not.