France relies on German gas and coal to stabilize their grid. You cannot power down or up a nuclear plant quickly and in the summer some rivers get too hot for cooling unless you want to kill all wildlife in it.

Germany is also importing a lot of nuclear power from France.

I'm not saying that Germany is in a better position than France but France couldn't live off of pure nuclear either. Both countries need each other (plus the rest of the European grids) to support their local grids. France is delivering a lot of the baseline power and Germany can help out in times of shortages and overproduction.