pessimists don't get promoted, but more importantly the most important skill is convincing your boss and the boss's boss that your course of action is the best path forward.

Any idea how they got away with this?

I think the generally acknowledged approach if you work on a trading desk at a bank want to put on some trade with desk-blowup potential is you first send out an email to your boss/head-of-desk outlying the trade and targets and stop loss and whatever, even if he sits right next to you. Once he replies in agreement, he's on the hook and you have the evidence. This makes it perfectly reasonable to argue that its the desk head's responsibility to make sure these kind of blowups don't happen. If head of trading also feels that head of desk wasn't exactly a stellar performer anyways, then poof he's gone. It just so happens in this case that they didn't want to replace headcount anyways so the trader next in line, the guy who actually blew the desk up, got promoted. Maybe it was just the bank I worked at but I saw enough of these charades and couldn't take the job seriously anymore. It was too much of a farce for me so I quite Lol, but hey I guess there are people who enjoy playing that game, nothing wrong with that.

That industry is relationship and influence driven.