This year geopolitics struck back and made the rational economic choice a poor one in retrospect.
You could've simply read the official Russian doctrine. "oil is for profits, gas is for political control" - they even published it on the web FFS.
It was the choice businesses made, because they believed it was the best way to make profit in the energy market. The EU agreed on emission quotas and set up the emission trade system, in order to let the market choose how to reduce emissions. The market chose natural gas, and the politicians allowed that, because they believed in the wisdom of the market.
And BTW this isn't just about the market - our state wanted to support nuclear but the EU sued it for unfair competition. Oh no, the German electricity producers might make less profit from their Russian gas, what would we do?!?!?
I'm not sure that's true. The EU (25%) as a whole has more nuclear energy than the US (19%). About half of EU countries use nuclear power, keeping in mind almost half of EU countries have less people than Massachusetts.
Remember, the EU doesn't generally run energy policy. The individual countries do. If anything, it was a lack of commitment to green energy that led to this.
In fact, looking at the figures, the only countries worldwide that get more energy from nuclear than the EU _and_ aren't part of the EU are Ukraine (55%), South Korea (28%), Switzerland (29%), and Armenia (25%). And both Switzerland and Ukraine are synchronised with the greater European grid!