The vast majority of 'Visa Overstays' are from countries that we require visa's from, hence the term 'Visa Overstay'.
People from countries on the VWP rarely overstay their visit; that is way we allow them to be on the program.
If the number overstays surpassed a certain percentage of that countries visitors, then that country is removed from the program. This happen just a few years ago. One country surpassed that percentage and they were removed form the program and now all their citizens require visas.