I think this is the main one. It's a form of price discrimination. Folks fall on a spectrum from willing to go to more trouble to get more money to not willing to go to any trouble at all. It's in the best interest of a company to pay a higher rate to the former than the latter, but you can hardly go around polling people and then adjusting their salary accordingly. So you favor policies that implicitly offer the higher salary to those who signal they demand it without having to offer a higher salary to all. It doesn't have to be that they perceive the former to be worth more. Even if both perform exactly the same it's still worth it to pursue a policy which allows you to price discriminate effectively.