You must believe everything you're told about America. Have you really never been?
I can't imagine what it's like to only know about America through people bitching on the internet.
I don't come across terribly many obese women in public. In workplaces, yes, there's a fucking lot of fatness, but fat people are like you. After the work day they go home and wallow in their own shame. Go outside to any avenue of entertainment and you'll find yourself among swarms of slender, attractive youths.
Appearance is highly stressed in America. Teenage and college age girls especially are under heavy pressure to maintain their figure and go to extreme lengths to preserve it.
Most of the fat people would be ineligible anyway, by age or whatnot.