I cannot fathom how anyone could possibly come to that conclusion.
This is so simple... I don't know why it is so hard to grasp.
Example A:
You are a girl playing soccer, you live in a country that is obsessed with women's soccer, there are leagues all across the country that feature intense tournaments, and high-intensity training camps. To compete in these tournaments means you are competing against the best, all the time. This has been going on for hundreds of years, and women's sports are just as highly respected as men's... resulting in women being taught from birth to compete just like men are.
Example B:
You are a girl playing soccer, you live in a country that thinks women shouldn't play sports and it doesn't support women's leagues or competitiveness at all. Women are taught from birth that they are supposed to be pretty and fragile, not competitive. You play in soccer tournaments and attend a few camps, but there are few girls participating, and a very low level of competition due to lack of support and zero competitive culture.
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Example A is a mythical country where women are encouraged to compete from birth, and Example B is pretty much every country in the world currently albeit to less of an extreme.
Which country is going to have more skilled female athletes?
Is this really that hard to grasp?