Publishers want to sell games. Games sell better if they are rated USK-16. USK-18 is already a bit worse, while a game landing on the Index is quite a loss. Even worse would be a game which is "banned". You are allowed to own those, but selling or promoting it is illegal.
Just take a look at Command and Conquer 3: There were two versions. One rated USK-16, featuring no blood or controverse weapons (Aurora bomb instead of atom bomb), and one rated USK-18, completely uncensored. Perfectly legal - and the way I would prefer for HoS, if 1C does not want it to be rated only USK-18.
Personnaly, I would prefer a system without Index and banned media. Instead, USK-18 games or FSK-18 films should be treated like pornography: No cuts, but seperated selling rooms you can only enter after prooving that you are atleast 18 years old.
