Let's see, what is the target audience of fashion channels?Of course, women.
It's also clear that women are more interested in fashion than men, they purchase more clothes or jewellery, they appear on the covers of famous magazines much often than men ! Have you ever seen the man who spent 6 hours, looking for the pair of shoes that suits his clothes perfectly?
And that's why, famous designers are much more interested in female models, so it's obvious that the demand on female models is higher and they earn much more than men.