The market is made up of individuals acting in their own self interest. Why would any individual not make hiring easier if they thought they could gain from it?

The market is made up of individuals acting in their own self interest. Why would any individual not make hiring easier if they thought they could gain from it? Note that Jim Crow/Davis Bacon/etc was a legal regime, a "must discriminate" set of laws to prevent people from acting in their own self interest. What such mechanism exists today preventing me from acting in my own interest?