During a boom, bankers over-leverage and lend too much to generate more short term profit, knowing that others are pursuing similar goals and when the bust happens, the system is in trouble, not just them. If a banker holds back for long term stability, he loses short term profits and he's in trouble. You know what bubble euphorias are like.
That is, during a boom, if a bank ensures long term stability, it has a problem now. Whereas if it doesn't, we have a problem later. This is logically and historically obvious yet it surprises every generation.
Socialism doesn't work except in the instances where it does. Capitalism does work except in the instances where it fails.