Actually quite a few countries do (65) about half are unrestricted like the US others like Australia, which recently change from unrestricted to restricted, are restricted, that is at least one parent most be a citizen or legal resident.
The following countries have unrestricted birthright citizenship: Antigua and Barbuda, Argentina, Barbados, Belize, Bolivia, Brazil, Canada, Chad, Child, Costa Rica, Cuba, Dominica, Ecuador, El Salvador, Fiji, Grenada, Guatemala, Guyana, Honduras, Jamaica, Lesotho, Mexico, Nicaragua, Panama, Paraguay, Peru, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, Tanzania, Trinidad and Tobago, Tuvalu, the United States, Uruguay, and Venezuela.
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.https://worldpopulationreview.com/country-rankings/countries-with-birthright-citizenship
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