It's a side-effect of this states'-rights idea that Europeans seem to find terribly confusing.

Hey! Perhaps France and Britain find this confusing, being the overly centralised, old nation states that they are, but we don't! We have a perfectly nice federal setup with a two-chamber parliament, thank you very much, one of whose chambers consists entirely of state representatives, with the number of seats of each state depending loosely on its population.

Of course, the German constitution came about while we were occupied by, among others, the Americans. So it's possible that you had something to do with it all along. :P