At many large organizations, there's even political pressures that keep employees from being let go early in their employment. If a hiring manager says yes to a

At many large organizations, there's even political pressures that keep employees from being let go early in their employment. If a hiring manager says yes to a candidate and they go through training/onboarding, there's a certain amount of clout to be lost if you jettison that employee early on. It is, instead, better for the manager to make the employee appear to be productive to make it seem like the manager did a good job in hiring. Team accomplishments can be embellished, stronger team members can cover for the weaknesses of weaker team members, but admitting that a decision you made was incorrect gets punished. It's obviously better to hire someone competent in the first place, but the next best alternative, for the manager, is to live with their bad hiring decision.