The gender wage gap does exist. It's simply a fact that women earn less than men. The real question then, is why. Is it because sexist managers pay women less money than men? Are women less likely to negotiate their offers as aggressively as men? Do women on average have to work longer to get promoted (and consequently earn salary raises) and why does this happen? Is it because women are more likely to pursue careers that pay less? Is it because men are seen as more attractive when their income goes up but this doesn't hold true for women? Are women and men just biologically inclined to pursue different career paths? Does the wage gap exist because women are more likely to work part-time? Is it because women are more likely to choose to prioritize child-rearing over their career? Is it because society expects women to prioritize motherhood? Is it because managers pay women less because they assume women will be less committed to their career?

Some of these possible reasons are obviously more concerning than others. If the gender wage gap is 100% due to less concerning reasons, such as women simply making the choice to prioritize motherhood over their career, then you could argue that while the gender gap exists it's not a societal problem that we need to address since it's not caused by institutional discrimination of any sort. The reality is a lot more complicated and nuanced, and it's probable that there are several reasons that can explain the gender gap, that don't necessarily compete with each other.