Why would a company / employer not want to make use of an recruitment agency or headhunt agency

Nobody forbids them... but they will have to bring their wallet with them!
Just a quick example;
-finding a candidate through a Headhunting agency
-candidate’s year income is 60,000.00= dollar (average position)
-costs payable by the employer about 20 to 25 percent of the annual salary if hired
-this means around 12,000.00= to 15,000.00= dollars + VAT to be paid to the headhunter agency..

Their advantage by doing it through our advantaged system (find your own personal through Go Head Hunt Yourself) is huge! Even if they would handout a reward of 6000.00= dollars. Even then, they still benefit!