America has a work culture that tends to glorify long hours. Many CEOs for instance, set an example that's difficult to match. People with demanding jobs find themselves cutting back on sleep in order to fit in a bare minimum family time or other activities.
But bad sleep habits are a very real issue. Julia Kirby at the Harvard Business Review has a fantastic chart that makes it clear that our dysfunctional sleep culture has real consequences. Even moderate fatigue can impact performance as much as alcohol impairment:
Sleep and alcohol chart
HBR

She argues that awareness of sleep health needs to be acknowledged by employers, and for it to become a part of corporate culture. That's an important point.
Smartphones mean that more and more people sleep next to their email inboxes, making it the last thing they see at night and the first they see in the morning, potentially causing stress and reducing sleep hours.
Even those employees who leave at 5 or 6 are expected to hop back on the laptop in the evening, or end up doing so just to keep up.
And in a still sluggish economic environment, more results are expected from fewer people, stretching many workdays into the evening.
On the surface, it seems beneficial to have employees so dedicated and hardworking that they're there late at night. But overall, it ends up decreasing performance and health.