I mean, maybe? Bremen, Hamburg, and Berlin are Länder (the German equivalent of states). You could certainly make an argument for, say, NYC being its own state; it'd be bigger than Delaware. But a lot of these things are historical accidents: West Virginia only exists because of the Civil War, California would certainly not be one state if founded now, while DC isn't a state at all. And given that the boundaries of the states are entrenched by the constitution there's a heavy status quo bias as to what might happen in the future.
Berlin is a state because (esp West-)Berlin kind of had to be one in the restructuring after WW2.
Bremen and Hamburg both were Free Cities in the Holy Roman Empire. More importantly, they were among the very few Free Cities that retained this status until and past the end of the HRE (1806). Being in the Hanseatic League helped establish their importance, but the League wasn't actually a major concern at that time anymore, and hadn't been for over a century, but they certainly played to that history (and e.g. added "Hansestadt" to their names, long after)
