Because there isn't a wage gap in the west.
It has been demonstrated time and time again that the 'wage gap' can be explained by a combination of: the degrees women take compared to men, women's assertiveness in asking for raises/promotions, the time they take off work (e.g. childbirth/care), their preferences in regard to working overtime and what periods of time they have off, the different jobs they have... you know, their choice.
The 'wage gap' in the sense that it does exist is entirely comprised of women's autonomous choice. If you want to close it, the best solution is to take away their choice. I wonder how long women in the west would put up with being forced to work on oil rigs, as bin-collectors, in the sewers, and spending overtime every night in the office?
Not long, is the answer.
If you really do believe it exists, ask yourself this - each employer can either have male employees, and pay them a dollar for whatever period of time, or he can have female employees, who he would pay 40% less. In a time with no shortage of unemployed people, why would any employer choose males in this scenario?