Women do earn less than men on average, but that is because women make different choices. There is no wage gap measured in terms of hours worked. Let's try with pictures first.
Women in the West, for the most part, can safely assume that men will provide for them, either through private arrangements like marriage, or through progressive taxation.
Since men work more hours and earn more money than women, they also contribute more to the taxbase, which liberal governments increasingly hand out to women. Men are forced to pay for women, whether they agree to do so or not. Men who vote for socially progressive governments are essentially agreeing to marry every woman in the country, and if you think marrying one woman is a risky deal, try marrying all of them!
Consider the situation in the Nordic countries, which boast some of the highest "gender equality" indexes in the world. Who are the makers, the creators, the builders, the generators of wealth? Mostly men. Women work in a bloated government bureaucracy doing what anthropologist/economist David Graeber calls "bullshit jobs", sucking up taxpayer dollars generated mostly by men. The Nordic countries boast no brilliant women entrepreneurs, scientists, inventors or leaders, or at least not more so than countries that are reluctant to create meaningless paper-shuffling jobs to employ all the liberal arts and women's studies majors colleges churn out. If college campuses were reduced to STEM degrees, they would be populated overwhelmingly by men.
This is not because women lack ability in STEM areas, it's because they lack interest. Jobs that require years of training, long hours, relentless devotion and dedication simply don't interest women. Sweden, the gold standard for gender equality, has "one of the highest percentages of women working part time anywhere in the world."
Women in rich countries work fewer hours and earn less money than men because they can. Men allow them the luxury. Travel to an emerging economy, like China, and the story looks very different. Fully 40% (and the number is moving upwards) of all engineers are women in China, because women there cannot rely on men to pay their way. A woman in China with a shot at a university spot knows that she has the opportunity to lift her entire family out of poverty, and if she wastes that opportunity studying ancient pottery, her family will remain in poverty. No men are going to come along and rescue them. So she makes the sane, rational choice to acquire highly valued labor market skills, just as men feel compelled to do in the West.
Women in the West don't have to do this. Even if she is poor, she is not responsible for her entire family's well-being. A Western woman is taught from birth that she is special and can do anything and is beholden to no one but herself. The West has a large social safety net to care for women who make stupid, irresponsible choices, funded by the predominantly male taxpayers. Men grow up with the understanding that they are going to need a job, will likely have to support a family on their own dime, and boots have straps for a reason. Many men are rejecting these obligations, for good reasons, but that doesn't change the fact the obligations are there to reject.
Women have no such obligation.
A woman in the West does not have to work a day in her life, if she chooses not to. Most women do want to work, but not at anything hard, dangerous, demanding and not for too many hours. Even when women choose a demanding career such as medical doctor, they approach the job in a completely different way than men do.
They spend more time with each patient; when choosing jobs, they are far more likely to cite time for family and flexible hours as "very important" and to prefer limited management responsibilities. Male doctors, on the other hand, are more likely to think about career advancement and income potential.
Who do you think earns more money? The man who undertook an extra decade of training to be a specialist, who works 60-70 hour weeks or the woman who works part-time as a family physician prescribing blood pressure medication and referring the difficult problems on to the more highly trained men? This is not misogyny, this is not oppression, this is not discrimination. This is women having the luxury of sucking up training spots and then refusing to work full hours because they don't have to. They become doctors then marry other doctors who work longer hours and make more money allowing them the luxury of working fewer hours.
It's called assortive mating (aka hypergamy), and it's having an enormous impact on the concentration of wealth and ability. The bottom line is that women still "marry up", which allows them the privilege of working only when they care to, at jobs requiring less skill, less training and less effort than the jobs their partners hold.
How ironic that all the bitching and moaning and weeping over the wage gap is actually proof that women in the West are some of the most pampered, indulged, entitled, coddled women in history. Most women recognize that, and refuse to get behind feminists who call indulgence "oppression". Feminism continues to shed numbers dramatically, and the pace of that will only increase.
If we really want to close the wage gap, then remove the social security net, downsize the government radically, forbid women from accessing their husband's income and put up a big banner saying:
Sink or Swim!
Funny, but I'm guessing that's not the kind of equality feminists are interested in. Too bad. It's where we are headed. Hey, feminists, are you beach body ready? You might want to stock up on that protein powder. You'll need the muscle mass when the waters rise. Get ready to swim.