Ich verstehe nicht

I do not understand the following:

there is a big problem with mold in houses here. There are handouts and directives on how to properly air out one's home to prevent mold. Literature about mold prevention notes that the mold occurs because of the way the houses are constructed. One has to open windows in a succession and it's advised to even air out one's comforter daily.

I can understand that this would happen in old houses. After all, there are houses here that are older than the country from which I hail.

I believe that the mold can happen in new houses, too. Here is the part that I do not understand: the Germans are great at engineering things. With new houses, why on earth wouldn't they change building techniques to minimize or avoid mold?! Why keep doing the same thing that doesn't work? I wonder what I am missing here.