People in managerial positions don't just want to be rewarded for their work. They want prestige and the root of almost all forms of prestige is nostalgia.
Nostalgia (and its attendant fallacies) leads to this long-hours glorification, because people who suffer a lot to push something through, after it succeeds (regardless of whether the suffering contributed) end up remembering the "glory days" of energy drinks and double-all-nighters as if those moments were better than they actually were. Those weren't fun at the time. That's a happy-ending reinterpretation because scary things that end well are often remembered positively.
What's missed is that (1) those crunches aren't sustainable, (2) they're only "glory days" for people who get major, career-improving and permanent benefits from the work-- otherwise it's just managerial abuse, and (3) most of those crunch-driven efforts fail and just become miserable death marches that make people really bitter, and the career damage of that can last years.
If people actually leave at 5:00, they recover better from those death-march episodes because they haven't let their health and network go to shit.