Why a stale pipeline costs money
It is tempting to think an inflated pipeline is harmless optimism. It is not. It distorts the forecast, which distorts hiring, stock and cash decisions. It hides the genuine shortage of new opportunities, because the total looks adequate. And it makes the list unreadable, so the deals that could actually be advanced receive the same attention as those that never will.
There is also a morale cost. A team that knows the pipeline is fiction stops using it as a working tool, which means the data quality degrades further, which makes the fiction worse. Cleaning it annually is partly a data exercise and partly a way of restoring the list to something people believe.