Germans are only acting like that because of Turkey's mistake to buy Russian tech. I mean seriously, who cares if the US didn't offer joint production or ToT with the Patriot. In the next 5-10 years Turkey would have produced its own indigenous systems to not really on partners for these 'crictical technologies'. Russian co-operation may result in slight benefit in the short term, but ultimately, its not worth losing credibility/support from Europe, let alone from the USA.
In Russia's eyes theres nothing to lose with providing such technological co-operation. But there's certainly significant gains. Its like the Sino-Soviet nuclear co-operation dilemma. Russia simply helped China build nuclear weapons/have access to Russia because they could use this as leverage against them. e.g. stalling or even shutting down operations in order to prolong China from 1) having access to such technologies 2) Prevent the inevitable, China pursuing its own independent path to nuclear proliferation - which, obviously, the Soviets would not be able to control.
In the same way, by Russia "helping" Turkey now, of course Turkey may have access to infrastructure e.g. space ports, but this would mean that 1) Turkey becomes dependent on Russia for such technologies 2) Russian can use this as leverage to hinder Turkish (independent) advancements 3) Russia can use this situation to 'monitor' its regional rival.
Germans are the one who are not stopping to buy gas from Russians, even with pressure from Americans. So why would they make a problem about S400?
Ther problem is EEZ dispute between Greece. Greece crying about Turkey.