Sunk cost fallacy. If you get to the point where pulling the plug means someone has gone bust, it's already over and you need to pull the plug sooner rather than later.
Well the folks at Credit Suisse aren’t perfectly rational beings either, it’s totally understandable why they behaved like that, most folks would engage in wishful thinking when staring at a multi billion dollar loss that hasn’t been realized yet (several hundred times their compensation).