Industrial companies have been the backbone of the German economy for the longest time. They provided decent living wages for a large section of the blue collar workforce.
The reality is that not everyone is built for a office job, not everyone has the skills, education or intellectual capacity to work in a service-based economy. Yet, these folks could make a decent living for themselves.
"Decent living" for the standards of year 2000 perhaps. Real wages stagnated for a long time while rich got relatively even richer. Furthermore, the structure of the economy has been changing, it's just that Germany is slow to adapt (perhaps more so because of its aging population).
Why should a rich country keep its industry and salaries flat for so long?