They are market leaders in some very high-margin things most people never think about, and interestingly they sell a lot in Asia, where one might expect them to be more vulnerable to competition. German Quality is a huge brand worldwide.
I also have a friend in Berlin who's sort of inheriting the family business, manufacturing something so random I always forget what it is. Involves rubber I think. High margins, privately-held family business, etc.
I really think a lot of these companies, if they were in the US, would either go public (the bigger ones) or be sold up to a bigger concern. But in Germany you'd have to pay a really big premium to get your hands on someone's multi-generational family business. As long as there are kids to inherit the factories then that's what they're gonna do.