Many employers hire recruiters for a variety of reasons.
Some companies with full personnel departments may turn to a recruiter after spending money on advertisements, job fairs, and their own recruiting efforts without success. Other companies may have been awarded a government contract and need to find highly qualified candidates quickly to avoid expensive penalties that would be levied against them if they don't begin work by a certain date. Smaller companies without personnel departments or budgets for extensive advertising campaigns look at recruiters as an outsourced arm of their human resources department. Then, there are those companies with proprietary information to protect, such as expansion plans, new technological developments, or intentions to replace key employees. By prescreening candidates, recruiters limit the amount of people to be interviewed who will be privy to sensitive information.