In a weird way, I think it was just a quirk of circumstances. We were a small team in a satellite office of a much larger company, which generally meant we were financially stable but otherwise disconnected from the rest of the company (no HR present or anything like that). So when someone misbehaved, it was sort of a "what happens in vegas stays in vegas" kind of thing, IE, as long as your shenanigans don't have ramifications outside of the group we'd keep things in the family.

I think because it was such a tight knit group, there was more tolerance than there would be in a more detached professional setting. I think this guy also got a lot more slack than he deserved because he was young and talented, so people chalked it up to immaturity.

That might be overcomplicating things though. I think when it came down to it, our boss was basically a nice person who didn't really want to fire anyone, and there was no pressure to, so he'd procrastinate it, and the rest of us didn't really want to see him fired, at least to the extent of outright advocating for it, and so it just sort of kept going until he finally left to do something else.