I think the problem is that the supply of veterans is not always assured to synchronize with the demand. The sorts of recruitment surges, and military ventures, that DOD engages in, and which provide that supply, are not intended to mesh with the staffing needs of the civilian side of the PS. And the policies that provide veterans' preference for all the right ethical reasons are drafted in a completely decontextualized way.
All too often, well-intentioned policies, oozing with face validity for all stakeholders, can run headlong into circumstances the policy did not anticipate.
Exasperating, yes, but whaddya gonna do?