Natural psychological differences between men and women that have evolved over millions of years in a tribal environment whereby men and women had different roles.

Men have an additional motivation to become successful because they become massively more attractive to women. The same isn't true the other way around.

A difference in the overall number of hours worked. It's a simple fact that men work more hours than women in total, but isn't factored into the pay gap at all. Ridiculous.

The fact that women tend to naturally be the primary caregivers of children and are more likely to take time off when they become mothers. You're a business owner who needs to decide who to hire, do you take the 31 year old woman who has a high chance of becoming a mother over the next few years? Who you'll the have to pay huge amounts of money to train and replace somebody to fill her position?

Or do you reduce the risk, and simply choose the 31 year old man instead? I know which I'd choose as a business owner in a competitive marketplace.

Are any of these things taken into account by the "pay gap"? Nope! It's simply assumed that it must all be down to sexism.