All German banks are required by law to identify their customers. The bank is subject to a heavy fine if the bank doesn't follow the law. The customer needs a valid German address. In order to have a valid and verifible German address you need to be registered ( Ordnungsamt) which means that you live in Germany. Even if you spend part of your time living in some other country i.e.
U.S. you still MUST bring your body to Germany at least once every 6 months or your residence is cancelled. Easier said than done.