It's pretty simple - the girls don't pay to use the sites - but men do. The sites say the girls are serious, but anybody can say that if they don't have to pay.
"1. Women don’t pay on Elenas Models - It’s free for ladies to join and communicate with men. They do not pay
to talk to guys, and can freely email to men or send them an EOI."
A Foreign Affair
"All our services are COMPLETELY FREE OF CHARGE for women!!!"
Just try signing up as a female. You won't be asked for money.
The reason the women don't pay is because the sites need their profiles, so men can pay the site to access them. That's much easier and more legit than creating a ton of fake profiles. In return for their real profiles, the women get obligation-free validation.