HBD besitzt zurzeit eine feste APR von 12% die monatlich ausgezahlt wird

It isn't a fixed rate, but is subject to change at any time by witness vote. I would not expect 12% "long term", I see this as more of a promotional offer as long as Hive and HBD are relatively small and unknown.

Currently, the benefits of increased exposure and attracting capital far outweigh the current cost of about 0.1% or so increased inflation. When that is no longer the case, over time the rate will shift to something more sustainable.