That is something different, but related.
Basically: To sell porn games in Germany you have to verify the age of the customer. Steam doesn't do this, at least not in a serious manner. Hence Steam blocking all porn games in Germany, so they don't have to change their age verification system.
The issue with things like FNAF 1-5 is that a lot of older games do not have any age rating set at all.
Just the developer setting their age rating to something valid will fix that issue.