Retaining Of Corps Members

Please i want to know why federal parastatals are not retaining corpers who served with them. I served with NTA and i wasnt retained either. Is it because of the embargo placed on federal jobs. I believe young graduates should be allowed to make inputs into the system, that way working with the ministry will be interesting. you find out that old and non vibrant people are the ones making the ministerial jobs uninteresting. Or what do you think?