The reason behind birthright citizenship, stems from prejudice against Black people, and the growing awareness that American citizenship is not about racial identity or the prior political affiliations of your family.
One cannot become French simply by becoming a French citizen, because they view nationality based on race and genetics. After the Civil War American society became increasingly aware that basing such things on race and genetics leads to racism. They passed the 14th amendment to solve the problem that resulted in former slaves, not being considered citizens, they didn’t just say former slaves are now citizens, because they intended to address the same problem from happening again with different ethnicities or national origins.
One cannot become French simply by becoming a French citizen, because they view nationality based on race and genetics. After the Civil War American society became increasingly aware that basing such things on race and genetics leads to racism. They passed the 14th amendment to solve the problem that resulted in former slaves, not being considered citizens, they didn’t just say former slaves are now citizens, because they intended to address the same problem from happening again with different ethnicities or national origins.