German here. There are a multitude of reasons... forgive me all the German sources please, but I don't really have the time to dig up English sources of the same quality.

First of all is the close history that the Social Democrats have with Russia, dating back to former Chancellor Willy Brandt and the Neue Ostpolitik, and renewed by the 1998-2006 former Chancellor Gerhard Schröder who initiated the Nord Stream 1 gas pipeline and infamously worked as a high-profile lobbyist for Gazprom after his period and is rumored to be a close personal friend of Vladimir Putin for years now.

Then we have the history of the 1968-era hippies, the peace movement and large parts of the radical left, which has to this day strong ties to the Green Party, the Left Party (which is the successor of the former GDR's ruling SED) and partially also to the Social Democrat Party. Many of my comrades are still stuck in the Cold War anti-imperialist mindset (where only the Western / NATO sphere is seen as an aggressor) and fail to see that both modern China and Russia are imperialist agents on their own. Hopefully the events of the last few days will wake up some of them, though.

And finally, the entire gas clusterfuck.

1) A lot of residential heating - not just in Germany by the way, but also across wide parts of Eastern Europe and Italy - depends on either gas or oil, as electric heating is ridiculously expensive (at >30 ct/kWh!).

2) electricity. The Conservative/Christian Democrat CDU, whose Chancellor Merkel ruled for the last 16 years before finally getting booted out of office last year, took pride in demolishing the domestic solar and wind turbine industry (the former by cutting subsidies which was followed by Chinese dumping taking over the market, the latter by imposing ridiculous zoning requirements [1]) and was happily accepting "donations" (aka legal bribery) from the fossil fuel industry, and their Bavarian sister party CSU (as well as a number of various local NIMBY movements, called "Bürgerinitiativen") keeps throwing impediments against high-power electric lines to expand the electric grid so that it can distribute Nothern German-generated wind power to the South (Bavaria and Baden-Württemberg). Combined with the phase-out of coal-fired plants and nuclear plants, gas peakers have risen in importance [2].

3) We don't have many alternatives as a continent to source gas from, other than pipelines. There are no LNG import terminals in Germany [3], we have to rely on the import capacity of the Netherlands, France and Belgium [4]. At the same time, the Dutch gas field at Groningen is suffering from earthquakes following the gas extraction [5], Norway doesn't have much spare capacity [6] and the UK only has enough gas reserves to make 42% of their own demand [7], not to mention the Brexit aftermath which included the UK getting booted off the EU energy market.

4) We have a lot of industry (especially petro-chemical and metal) relying on gas for energy and as a raw material. About a third of industrial energy consumption is gas-based [8].

We are in a "perfect storm" situation, and now over 40 years of lackluster politics across the board are crashing down on our head.

[1]: https://www1.wdr.de/nachrichten/landespolitik/windraeder-abs...

[2]: https://www.tagesschau.de/wirtschaft/deutschland-braucht-neu...

[3]: https://www.tagesspiegel.de/wirtschaft/knappe-gaslieferungen...

[4]: https://www.tagesschau.de/wirtschaft/technologie/lng-termina...

[5]: https://www.deutschlandfunk.de/gasfoerderung-in-den-niederla...

[6]: https://www.zdf.de/nachrichten/politik/norwegen-regierungsch...

[7]: https://www.zeit.de/wirtschaft/2021-09/gaspreis-grossbritann...

[8]: https://www.destatis.de/DE/Presse/Pressemitteilungen/2021/12...