Occupied French yards could not simply expand German output

Why did Germany not use French naval infrastructure and designs to expand shipbuilding?

Yards alone were insufficient because Germany lacked a reliable, cooperative skilled workforce and could not easily verify complex work such as welding.

The slow completion of even a Flower-class corvette shows that physical facilities did not automatically translate into output. Warship construction depends on skilled people performing thousands of difficult tasks to a trusted standard. An unwilling welder could produce defects that were extremely hard to detect with wartime inspection methods. Coercing or killing workers would only shrink the labor pool further. Conquered industrial plant cannot be counted like an intact domestic production line.