It's not regulations that are the problem. They were obviously using this bank as a free margin account using customers money to leverage their debts. They did it because they have a lot of money to win when betting with other people's money and only 100% to lose.
10x margin and the government making your counterparty whole if you fail?
Of course this degenerate bank used it in the most VC way.
Don't make a single client of them whole. Those banking there probably had connections to the people making tons of money when the bets went their way. Those who recommended banking there need to lose their credibility.
The risk they took was not a mistake. It was a feature. It was intended.