Many, many, many factors. Education, types of jobs, company's investment in their employees. This is not a socialist society where everyone makes the same. I work in IT and women make less in IT because they refuse to go into STEM. They work less hours, refuse to travel, want better benefits. A woman can leave a career\job any god damn time to have a baby. A company is going to have to pay someone else for this missed time and 75% of the time these women never come back. And that's just one small example. Men go into more dangerous jobs by far, men die at\from more dangerous jobs by like 90%. Just another small fact. And there many other facts. real life facts.