If the guy at the next desk over stays an hour later than you every day, he'll look like he's working harder, so he'll be less likely to get laid off. Once you have multiple people thinking that way and no opposing structure to encourage cooperation, you get a classic status arms race.

This, plus the known fact that most nerds can't cooperate. So even when some programmers start noticing the pattern, there is always some idiot who just cannot resist the opportunity to show everyone how smart he is by volunteering to work harder and longer, in worse environment, etc.