This happens because high costs that are not easily measurable (such as the productivity hit from interviewing candidates) don't show up on spreadsheets and thus don't result in recriminations from on high. But the relatively low, one-time cost of a new hire shows up immediately on the spreadsheet and that means whoever did the hiring is going to get yelled at for paying too much. Given this incentive structure, it makes sense to drag out the hiring process as long as possible.