I have fought for raises of colleagues who were more introverted or just didn't feel as comfortable going into the pit and haggling for an appropriate raise. I saw the wage gap increase because they sometimes just didn't know how far ahead others were in terms of wage.

Keeping individual wages a secret ultimately benefits the employer as they can use the knowledge disparity to their advantage.

I even know of arguments that a new father doesn't need to receive a relevant raise as he is extremely unlikely to switch jobs due to the newborn.

Employers, even most of the ones claiming to be fair, will do everything to keep employees in the dark regarding fair pay.