Why does can only the national government have the right to take away someone's citizenship?

Only the national government has the right to take away someone's citizenship because citizenship is a legal status defined by national law, which grants individuals specific rights and privileges. This authority is rooted in the principle of sovereignty, allowing the national government to regulate who belongs to its political community. Additionally, depriving someone of citizenship typically involves significant legal and constitutional implications, necessitating a centralized decision-making process to uphold consistent standards and protections.