If salaries are so hard to judge, why is it that people think it's obvious when there is a studying saying there is supposed wage gap between sexes? It seems l

If salaries are so hard to judge, why is it that people think it's obvious when there is a studying saying there is supposed wage gap between sexes? It seems like the skepticism goes only one way, which is when the study says that wage gap between sexes is negligible. [edited for grammar]