Oil, coal, fertilizer are commodities. One can ship these things from anywhere in the world. There are many producers and many customers. What Germany doesn’t buy, someone else will, and that frees up supplies from other sources. No problem for either side.
But Gas is not really a commodity. It requires long term relationships between partners that trust each other. Russia under Putin started acting “whimsical” in its relationships abroad well over a decade ago. And its gotten much worse.
Would Russia and Putin acting whimsical happened to coincide with the United States building biological labs in the Ukraine?