US has dished out far more severe punishments for this stuff than the Bundesnetzagentur could https://www.justice.gov/opa/pr/24-defendants-sentenced-multi...
This is not about regulations, lots of these robocallers are straight up criminal operations who will not be swayed by fines.
If Germany has implemented some technical measures against robocalling I'd absolutely love to hear about them! I seriously doubt they have though.