A lot of traders work long hours to feel better about themselves. Usually the ones who consistently stay late are either using inappropriate technology or are compensating for some other inadequacy. They also tend to have the worst performance in the end and ultimately leave (not always voluntarily).
I would love to see some counter-examples where 90 hour weeks actually do power superior performance: investment banking
I work at the second largest investment bank in the world and have not seen anyone work 90 hour weeks. The traders may work 7am-6pm, but that's only 55 hours. Everyone else works somewhere around 40 hours.