While clearly there are diminishing returns on the number of hours worked in a day, the limit of productivity is way higher than 8. I'd guesstimate that the average person can do 10 solid hours, working on 75% for another 2, and 50% after that. That doesn't mean your work is only 50% as good, you just start slowing down.

And I'm including small off task sessions in that time. When these guys say 100 hours, they aren't stopping the clock when they are reading an article on ESPN.

I know several engineers and programmers who are doing over 10 a day.

People vary on how much they need to sleep, but I really doubt they are only getting 3-4 nights for months at a time. 100 hours a week gets you almost 10 hours a day off. They live close to work, eat takeout at work, get people to do their housemaking duties. That leaves enough for 5-7 a night. I'm sure less on weekdays and more on weekends.

As to why programmers are more sensitive to work/life balance, it's probably because the programming industry has been hot for a long time. Plus, programmers are extremely productive because of how software scales. But industries just develop different cultures. Many tech companies compete for talent based on perks, but finance is mostly based on money.

There is also a bit of hazing element to the finance industry hierarchy. You work less as you guy up. The time is sort of "paying your dues." The ones doing 100 hours are 21-23 years old and can still handle it.

In consulting and law, the billable hour creates perverse incentives. I can be twice the lawyer than someone who bills 15% more hours, but they are 15% more profitable.

Finally, a lot of people can't hack it. The burn out rate in big banks is absurd. The average person lasts less than two years I believe.