If it doesn't cost the company significantly extra (say, due to overtime), then the company's interest is increasing work hours for everyone to the max. In such a situation, other workers doing so, and getting discretionarily rewarded for it simply erodes the position of those who, rightfully, refuse to work more than they need to.

Unless there's a fixed "here's how much extra you will be rewarded, and thus how much it will cost the company" policy about working past normal working hours, people who do so are scabs.