One of the reasons they judged this way is the lack of feasible low-carbon alternatives. Which is hilarious because we're talking about EU taxpayer money here. Money that can be spend only once. If you spend it on a nuclear reactor which may or may not be build within 10 years, you can't spend it on those "feasible low-carbon alternatives" which we already have and which would have produced a lot of energy in that construction time.
The court however said also, that the strict regulations, which are often the main argument of nuclear fans, are not to be lowered. Therefore there is no outcome for nuclear where it will get cheaper. The French, which have never stopped building nuclear all over the world, still didn't manage to get it cheaper. There are always cost explosions which cause the energy price to rise over time.
Which brings us back to why we're even talking about this:
France has a fleet which needs more and more maintenance. It is costly and the state already supports every Watt of nuclear energy through their tarif bleu. They desperately need this EU money to support this show. Without it, they'd be forced to innovate and expand on renewables, like the rest of the planet.
...but just like the Germans with their fossil fuel cars, they'll try to keep it alive as long as possible, even though the market comes apart around them.