I think that there's an excitement, almost a cocaine high from hiring new employees. Supervisors get a rush and jolt of energy from having newbies onboard, but this energy quickly fades as they new employees may be 'harmonized' and swallowed by the overbearing company culture and workload. Managers then begin to look for that new freshman on the horizon, all while the slightly more experienced staff are walking out the door. It's an unsustainable cycle.