The Berlin government considers it a legitimate reason, and since they get to make the rules that's all that matters in this case. If the people of Berlin would

The Berlin government considers it a legitimate reason, and since they get to make the rules that's all that matters in this case. If the people of Berlin would disagree, it's up to them to elect a new government with different views on the topic. "I want to move to Berlin", on the other hand, is not a particularly legitimate reason to kick out a current resident for a newcomer.