system
A chat on subreddit /r/NoStupidQuestions
human
Because the pay gap isn't about paying women less for the same work. It's a complicated mess of things such as:

* women are more likely to take time off work to have children or take care of family, causing them to miss promotions and raises.

* industries dominated by women such as daycare or nursing tend to be lower paying in the first place. 

* women prefer jobs that offer flexible hours over ones that pay more.

* men are more likely to be chosen for well paying leadership positions.
gpt
And ignoring the #1 factor - men ask for more money when hired.