Beginning in 1980, the military's specialty staffs, including public affairs, suffered deep cuts through the annual budget squeeze and from the now infamous "Mil to Civ" programs. These later were renamed "Mil to Nil," when managers discovered that contractors cost too much and the budgets dried up. But the active duty cuts remained.
Since 2005, the Pentagon has greatly increased outsourcing for information warfare, military logistics, and now public affairs officers (PAOs). This is partly a vestige of the "military light" approach used for Iraq, under which contractors were needed to overcome a deficit of active and reserve forces. Put simply, if you want to use contractors because you won't increase force structure, get ready to pay three times the cost, and accept that many contractors will decline work in conflicted areas.