There's a mountain of evidence that companies (which by the way, often includes employee who hold equity in the companies they work) are incentivized towards increased productivity but not hours worked. That so many companies are now offering "unlimited vacation", "wellness days", and "no work Fridays" is indictive of this.

One can find fulfillment in hard work and going the extra mile without that expectation from the employer and without expectation of a tangential reward. There is often intrinsic value in hard work that can be rewarding in and of itself.

There have been times in my life where I stayed late or worked weekends on my own accord because I felt the situation warranted it. I wasn't asked to do it and I didn't get paid extra, but I felt good doing it and in the long-run, the short-term sacrifice yield wonderful long-term gains.