They are part of EU. They could dissent from subservience to USA like Hungary, which would be in their own interest but they didn't. Also it's not a fucking embargo or sanction, Gazprom just want another currency and is even offering to setup the deal to make it easier. I mean it isn't really strange in any commodity exchange? Compare this with the criminal sanctions USA are impposing on the countries.

The reason is simple, they played the stupid game of imperialism against themselves and now won stupid prize.