You assume incorrectly, only the first 5 where the American citizens. Three of the Americnas weren't immigrants or dual citizens, and AFAIK were native born Americans. Only one was dual citizen of Israel, Dina Carter. As I recall the one with dual French citizenship was born in France of American parents. The procedure in such cases is to register the birth with the US embassy, but often the country in question still considers the child to be one of theirs too. It's slightly different if one of the parents is US military stationed in the host country.
Other than Carter, they were just students, studying abroad. But then they were just Jews, so I guess that's enough to claim their citizenship was "dubious".