Starting with Ford for line workers in production, we know that long hours are not equal to quality. They know it in these law firms, software companies, basically nearly everywhere (people are not stupid).

So why this still done like that? Because it easier to answer the question: "How many hours have you been working this week?" than "What value have you brought to the company this week?"

We substitute an easy question to a harder one and we feel we answered the hard one.

Edit: Fixed grammar/typos