It's all politics, and sadly politicians would much rather shut down a perfectly fine airfield to make room for building shopping malls and condos.
The public opinion ain't very favourable either. People like quiet neighborhoods, airports are noisy, and private jets very unnecessary and only for the super-rich. No thank you, nobody needs that.
Germany (Munich, Berlin...) have mostly lost the battle, keep the fight for GA airfields going where you can. Zurich for example - Dubendorf may still not yet be completely lost and maybe even at some point in time take over the GA traffic from Zurich. Not that it will be easy to integrate it in the current ATC system, and again, there's still public opinion, but still...