What does the (mis)management of a public infrastructure project have to do with Germany's attractiveness as a base for manufacturing?

Everything?

Plants don't pop up overnight to the obliviousness of the state. This proposal brings into consideration vast amounts of money, tax revenue, and employment opportunities that the government will care about. All with unique infrastructure requirements and long roadplans.

To flip the question around: what does the ability to produce executive cars have to do with Germany's ability to fix the problem Intel have been stuck on for the better part of a decade?

The lead of construction for BER was a dutch company

Imtech? It was their German branch. Regardless, at least they could rely on Siemens and Bosch to nail the fire system, PG BBI to do the planning, and GMP for the architecture.